Earth and Sky Every Child Should Know - Easy studies of the earth and the stars for any time and place

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Title: Earth and Sky Every Child Should Know - Easy studies of the earth and the stars for any time and place
Author: Rogers, Julia Ellen
Language: English
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[Illustration: Pike's Peak, Colorado]

EARTH and SKY EVERY
CHILD SHOULD KNOW

EASY STUDIES OF THE EARTH AND THE
STARS FOR ANY TIME AND PLACE

JULIA ELLEN ROGERS

AUTHOR OF
"THE TREE BOOK," "THE SHELL BOOK," "KEY TO THE NATURE
LIBRARY," "TREES EVERY CHILD SHOULD KNOW."

ILLUSTRATED BY
THIRTY-ONE PAGES OF PHOTOGRAPHS AND DRAWINGS

[Illustration]

NEW YORK
GROSSET & DUNLAP
PUBLISHERS

PUBLISHED, OCTOBER, 1910

ACKNOWLEDGMENTS

A number of the photographs in this volume are used by permission of the
American Museum of Natural History. The star maps and drawings of the
constellations are by Mrs. Jerome B. Thomas. The poem by Longfellow,
quoted in part, is with the permission of the publishers, Houghton,
Mifflin & Co.

* * * * *

CONTENTS

_PART I. THE EARTH_

PAGE

THE GREAT STONE BOOK 3

THE FOSSIL FISH 6

THE CRUST OF THE EARTH 9

WHAT IS THE EARTH MADE OF? 14

THE FIRST DRY LAND 22

A STUDY OF GRANITE 27

METAMORPHIC ROCKS 31

THE AIR IN MOTION 35

THE WORK OF THE WIND 44

RAIN IN SUMMER, _by Henry W. Longfellow_ 50

WHAT BECOMES OF THE RAIN? 51

THE SOIL IN FIELDS AND GARDENS 58

THE WORK OF EARTHWORMS 63

QUIET FORCES THAT DESTROY ROCKS 68

HOW ROCKS ARE MADE 72

GETTING ACQUAINTED WITH A RIVER 78

THE WAYS OF RIVERS 84

THE STORY OF A POND 90

THE RIDDLE OF THE LOST ROCKS 93

THE QUESTION ANSWERED 96

GLACIERS AMONG THE ALPS 98

THE GREAT ICE SHEET 104

FOLLOWING SOME LOST RIVERS 110

THE MAMMOTH CAVE OF KENTUCKY 114

LAND BUILDING BY RIVERS 121

THE MAKING OF MOUNTAINS 126

THE LAVA FLOOD OF THE NORTHWEST 130

THE FIRST LIVING THINGS 134

AN ANCIENT BEACH AT EBB TIDE 138

THE LIME ROCKS 147

THE AGE OF FISHES 152

KING COAL 155

HOW COAL WAS MADE 160

THE MOST USEFUL METAL 167

THE AGE OF REPTILES 175

THE AGE OF MAMMALS 180

THE HORSE AND HIS ANCESTORS 186

THE AGE OF MAN 194

_PART II. THE SKY_

EVERY FAMILY A "STAR CLUB" 201

THE DIPPERS AND THE POLE STAR 207

CONSTELLATIONS YOU CAN ALWAYS SEE 213

WINTER CONSTELLATIONS 219

ORION, HIS DOGS, AND THE BULL 223

SEVEN FAMOUS CONSTELLATIONS 231

THE TWENTY BRIGHTEST STARS 239

HOW TO LEARN MORE 241

ILLUSTRATIONS

Pike's Peak _Frontispiece_

FACING PAGE

Sand Dunes in Arizona 44

Grand Cañon of the Colorado 45

Castles Carved by Rain and Wind 52

Where All the Water Comes From 53

The Richest Gold and Silver Mines 72

Rocks Being Ground to Flour 73

A Pond Made by a Glacier 88

The Struggle Between a Stream and Its
Banks 89

Ripple Marks and Glacial Striæ 102

Glacial Grooves and Markings 103

Crinoid and Ammonite 140

Fossil Corals, Coquina, Hippurite Limestone 141

Fossil Fish 152

Meteorite 153

Eocene Fish and Trilobite 156

How Coal Was Made 157

Banded Sandstone. Opalized Wood 176

Allosaurus 177

A Three-horned Dinosaur 178

Remains of Brontosaurus 179

Restoration of Brontosaurus 182

Ornitholestes, a Small Dinosaur 183

A Mammoth 186

An Ancestor of the Horse 187

Orion, His Dogs, and the Bull 214

Other Fanciful Sketches of Constellations 215

The Sky in Winter 244

The Sky in Spring 244

The Sky in Summer 244

The Sky in Autumn 244

PART I

THE EARTH

* * * * *

THE GREAT STONE BOOK

"The crust of our earth is a great cemetery where the rocks
are tombstones on which the buried dead have written their
own epitaphs. They tell us who they were, and when and where
they lived."--_Louis Agassiz._

Deep in the ground, and high and dry on the sides of mountains, belts of
limestone and sandstone and slate lie on the ancient granite ribs of the
earth. They are the deposits of sand and mud that formed the shores of
ancient seas. The limestone is formed of the decayed shells of animal
forms that flourished in shallow bays along those shores. And all we
know about the life of these early days is read in the epitaphs written
on these stone tables.

Under the stratified rocks, the granite foundations tell nothing of life
on the earth. But the sea rolled over them, and in it lived a great
variety of shellfish. Evidently the earliest fossil-bearing rocks were
worn away, for the rocks that now lie on the granite show not the
beginnings, but the high tide of life. The "lost interval" of which
geologists speak was a time when living forms were few in the sea.

In the muddy bottoms of shallow, quiet bays lie the shells and skeletons
of the creatures that live their lives in those waters and die when they
grow old and feeble. We have seen the fiddler crabs by thousands on
such shores, young and old, lusty and feeble. We have seen the rocks
along another coast almost covered by the coiled shells of little gray
periwinkles, and big clumps of black mussels hanging on the piers and
wharfs. All these creatures die, at length, and their shells accumulate
on the shallow sea bottom. Who has not spent hours gathering dead shells
which the tide has thrown up on the beach? Who has not cut his foot on
the broken shells that lie in the sandy bottom we walk on whenever we go
into the surf to swim or bathe?

Read downward from the surface toward the earth's centre--

TABLE OF CONTENTS

------+----------------------+-----------+-----------------------
Part | _Rock Systems_ | _Dominant | _Dominant Plants_
| | Animals_ |
------+----------------------+-----------+-----------------------
VII. | Recent | Man | Flowering kinds
|{ Quaternary | |
VI. | { Pliocene | Mammals | Early flowering
|{ Tertiary { Miocene | |
| { Eocene | |
V. | Mesozoic | Reptiles | Cycads
IV. | Carboniferous | Amphibians| Ferns and Conifers
III. | Devonian | Fishes | Ferns
II. | Silurian | Molluscs | Seaweeds
I. | Fire-formed | No life | No life
------+----------------------+-----------+-----------------------

It is by dying that the creatures of the sea write their epitaphs. The
mud or sand swallows them up. In time these submerged banks may be left
dry, and become beds of stone. Then some of the skeletons and shells
may be revealed in blocks of quarried stone, still perfect in form after
lying buried for thousands of years.

The leaves of this great stone book are the layers of rock, laid down
under water. Between the leaves are pressed specimens--fossils of
animals and plants that have lived on the earth.

THE FOSSIL FISH

I remember seeing a flat piece of stone on a library table, with the
skeleton of a fish distinctly raised on one surface. The friend who
owned this strange-looking specimen told me that she found it in a stone
quarry. She brought home a large piece of the slate, and a stone-mason
cut out the block with the fish in it, and her souvenir made a useful
and interesting paper-weight.

The story of that fish I heard with wonder, and have never forgotten. I
had never heard of fossil animals or plants until my good neighbour
talked about them. She showed me bits of stone with fern leaves pressed
into them. One piece of hard limestone was as full of little sea-shells
as it could possibly be. One ball of marble was a honeycombed pattern,
and called "fossil coral."

The fossil fish was once alive, swimming in the sea, and feeding on the
things it liked to eat, as all happy fishes do. Near shore a river
poured its muddy water into the sea, and the sandy bottom was covered
with the mud that settled on it. At last the fish grew old, and perhaps
a trifle stupid about catching minnows. It died, and sank to the muddy
floor of the sea. Its horny bones were not dissolved by the water. They
remained, and the mud filtered in and filled all the spaces. Soon the
fish was buried completely by the sediment the river brought.

Years, thousands of them, went by, and the layer of mud was so thick and
heavy above the skeleton of the fish that it bore a weight of tons
there, under the water. The close-packed mud became a stiff clay. After
more thousands of years, the sea no longer came so far ashore, for the
river had built up a great delta of land out of mud. The clay in which
the fish was hidden hardened into slate. Water crept down in the loose
upper layers, dissolving out salt and other minerals, and having harder
work to soak through, the lower it went. The water left some of the
minerals it had accumulated, calcium and silica and iron, in the lower
rock beds, making them harder than they were before, and heavier and
less porous.

When the river gorge was cut through these layers of rock, the colour
and thickness of each kind were laid bare. Centuries after, perhaps
thousands of years, indeed, the quarrymen cut out the layers fit for
building stones, flags for walks and slates for roofing. In the
splitting of a flagstone, the long-buried skeleton of the fish came to
light.

Under our feet the earth lies in layers. Under the soil lie loose beds
of clay and sand and gravel, and under these loose kinds of earth are
close-packed clays, sandstones, limestones, shales, often strangely
tilted away from the horizontal line, but variously fitted, one layer to
another. Under these rocks lie the foundations of the earth--the
fire-formed rocks, like granite. The depth of this original rock is
unknown. It is the substance out of which the earth is made, we think.
All the layered rocks are made of particles of the older ones, stolen by
wind and water, and finally deposited on the borders of lakes and seas.
So our rivers are doing to-day what they have always done--they are
tearing down rocks, grinding and sifting the fragments, and letting them
fall where the current of fresh water meets a great body of water that
is still, or has currents contrary to that of the river.

Do you see a little dead fish in the water? It is on the way to become a
fossil, and the mud that sifts over it, to become a layer of slate.
Every seashore buries its dead in layers of sand and mud.

THE CRUST OF THE EARTH

It is hard to believe that our solid earth was once a ball of seething
liquid, like the red-hot iron that is poured out of the big clay cups
into the sand moulds at an iron foundry. But when a mountain like
Vesuvius sets up a mighty rumbling, and finally a mass of white-hot lava
bursts from the centre and streams down the sides, covering the
vineyards and olive orchards, and driving the people out of their homes
in terror, it seems as if the earth's crust must be but a thin and frail
affair, covering a fiery interior, which might at any time break out.
The people who live near volcanoes might easily get this idea.

But they do not. They go back as soon as the lava streams are cooled,
and rebuild their homes, and plant more orchards and vineyards. "It is
_so_ many years," say they to one another, "since the last bad eruption.
Vesuvius will probably sleep now till we are dead and gone."

This is good reasoning. There are few active volcanoes left on the
earth, compared with the number that were once active, and long ago
became extinct. And the time between eruptions of the active ones grows
longer; the eruptions less violent. Terrible as were the recent
earthquakes of San Francisco and Messina, this form of disturbance of
the earth's crust is growing constantly less frequent. The earth is
growing cooler as it grows older; the crust thickens and grows stronger
as centuries pass. We have been studying the earth only a few hundred
years. The crust has been cooling for millions of years, and
mountain-making was the result of the shrinking of the crust. That
formed folds and clefts, and let masses of the heated substance pour out
on the surface.

My first geography lesson I shall never forget. The new teacher had very
bright eyes and _such_ pretty hands! She held up a red apple, and told
us that the earth's substance was melted and burning, inside its crust,
which was about as thick, in proportion to the size of the globe, as the
skin of the apple. I was filled with wonder and fear. What if we
children jumped the rope so hard as to break through the fragile shell,
and drop out of sight in a sea of fiery metal, like melted iron? Some of
the boys didn't believe it, but they were impressed, nevertheless.

The theory of the heated interior of the earth is still believed, but
the idea that flames and bubbling metals are enclosed in the outer layer
of solid matter has generally been abandoned. The power that draws all
of its particles toward the earth's centre is stated by the laws of
gravitation. The amount of "pull" is the measure of the weight of any
substance. Lift a stone, and then a feather pillow, much larger than
the stone. One is strongly drawn to the earth; the other not. One is
_heavy_, we say, the other _light_.

If a stone you can pick up is heavy, how much heavier is a great boulder
that it takes a four-horse team to haul. What tremendous weight there is
in all the boulders scattered on a hillside! The hill itself could not
be made level without digging away thousands of tons of earth. The
earth's outer crust, with its miles in depth of mountains and level
ground, is a crushing weight lying on the heated under-substance. Every
foot of depth adds greatly to the pressure exerted upon the mass, for
the attraction of gravitation increases amazingly as the centre of the
earth is approached.

It is now believed that the earth is solid to its centre, though heated
to a high degree. Terrific pressure, which causes this heat, is exerted
by the weight of the crust. A crack in the crust may relieve this
pressure at some point, and a mass of substance may be forced out and
burst into a flaming stream of lava. Such an eruption is familiar in
volcanic regions. The fact that red-hot lava streams from the crater of
Vesuvius is no proof that it was seething and bubbling while far below
the surface.

Volcanoes, geysers, and hot springs prove that the earth's interior is
hot. The crust is frozen the year around in the polar regions, and never
between the Tropics of Cancer and Capricorn. The sun's rays produce our
different climates, but they affect only the surface. Underground, there
is a rise of a degree of temperature for every fifty feet one goes
down. The lowest mine shaft is about a mile deep. That is only one
four-thousandth of the distance to the earth's centre.

By an easy computation we could locate the known melting-point for
metals and other rock materials. But one degree for each fifty feet of
depth below the surface may not be correct for the second mile, as it is
for the first. Again, the melting-point is probably a great deal higher
for substances under great pressure. The weight of the crust is a burden
the under-rocks bear. Probably the pressure on every square inch reaches
thousands of tons. Could any substance become liquid with such a weight
upon it, whatever heat it attained? Nobody can answer this question.

The theory that volcanoes are chimneys connecting lakes of burning lava
with the surface of the earth is discredited by geologists. The weight
of the overlying crust would, they think, close such chambers, and
reduce liquids to a solid condition.

Since the first land rose above the sea, the crust of the earth has
gradually become more stable, but even now there is scarcely a day when
the instruments called seismographs do not record earthquake shocks in
some part of the earth; and the outbreaks of Vesuvius and Ætna, the
constant boiling of lava in the craters of the Hawaiian Islands and
other volcanic centres, prove that even now the earth's crust is very
thin and unstable. The further back in time we go, the thinner was the
crust, the more frequent the outbursts of volcanic activity, the more
readily did wrinkles form.

The shores of New Jersey and of Greenland are gradually sinking, and the
sea coming up over the land. Certain parts of the world are gradually
rising out of the sea. In earlier times the rising or the sinking of
land over large areas happened much more frequently than now.

WHAT IS THE EARTH MADE OF?

"Baking day" is a great institution in the comfortable farm life of the
American people. The big range oven is not allowed to grow cold until
rows of pies adorn the pantry shelves, and cakes, tarts, and generous
loaves of bread are added to the store. Cookies, perhaps, and a big pan
full of crisp, brown doughnuts often crown the day's work. No gallery of
art treasures will ever charm the grown-up boys and girls as those
pantry shelves charmed the bright-eyed, hungry children, who were
allowed to survey the treasure-house, and sample its good things while
they were still warm.

You could count a dozen different kinds of cakes and pies, rolls and
cookies on those pantry shelves, yet several of them were made out of
the same dough. Instead of a loaf of bread, mother could make two or
three kinds of coffee cake, or cinnamon rolls, or currant buns, or
Parker-House rolls. Even the pastry, which made the pies and tarts, was
not so different from the bread dough, for each was made of flour, and
contained, besides the salt, "shortening," which was butter or lard.
Sugar was used in everything, from the bread, which had a
table-spoonful, to the cookies, which were finished with a sifting of
sugar on top.

How much of the food we eat is made of a very few staple
foodstuffs,--starch, sugar, fats! So in the wonderful earth and all that
grows out of it and lives upon it. Only seventy different elements have
been discovered, counting, besides the earth, the water and the air, and
even the strange wandering bodies, called meteorites, that fall upon the
earth out of the sky. Like the flour in the different cakes and pies,
the element carbon is found in abundance and in strangely different
combinations. As a gas, in combination with oxygen, it is breathed out
of our lungs, and out of chimneys where coal and wood are burned. It
forms a large part of the framework of trees and other plants, and
remains as charcoal when the wood is slowly burned under a close
covering. There is a good proportion of carbon in animal bodies, in the
bones as well as the soft parts, and carbon is plentiful in the mineral
substances of the earth.

The chemist is the man who has determined for us the existence and the
distribution of the seventy elements. He finds them in the solid
substances of the globe and in the water that covers four-fifths of its
surface; in the atmosphere that covers sea and land, and in all the
living forms of plants and animals that live in the seas and on the
land. By means of an instrument called the spectroscope, the heavenly
bodies are proved to be made of the same substances that are found in
the rocks. The sun tells what it is made of, and one proof that the
earth is a child of the sun is in the fact that the same elements are
found in the substance of both.

Of the seventy elements, the most important are these: Oxygen, silicon,
aluminum, iron, manganese, calcium, magnesium, potassium, sodium,
carbon, hydrogen, phosphorus, sulphur, chlorine, nitrogen.

_Oxygen_ is the most plentiful and the most important element. One-fifth
of the air we breathe is oxygen; one-third of the water we drink. The
rock foundations of the earth are nearly one-half oxygen. No fire can
burn, no plant or animal can grow, or even decay after it dies, unless
oxygen is present and takes an active part in each process. Strangely
enough, this wonderful element is invisible. We open a window, and pure
air, rich in oxygen, comes in and takes the place of the bad air but we
cannot see the change. Water we see, but if the oxygen and the hydrogen
which compose the colourless liquid were separated, each would become at
once an invisible gas. The oxygen of solid rocks exists only in
combination with other elements.

_Silicon_ is the element which, united with oxygen, makes the rock
called quartz. On the seashore the children are busy with their pails
and shovels digging in the white, clean sand. These grains are of
quartz,--fine crystals of a rock which forms nearly three-quarters of
the solid earth's substance. Not only in rocks, but out here in the
garden, the soil is full of particles of sand. You cannot get away from
it.

_Aluminum_ is a light, bluish-white metal which we know best in
expensive cooking utensils. It is more abundant even than iron, but
processes of extracting it from the clay are still expensive. It is
oftenest found in combination with oxygen and silicon. While nearly
one-tenth of the earth's crust is composed of the metal aluminum,
four-fifths and more is composed of the minerals called silicates of
aluminum--oxygen, silicon, and aluminum in various combinations. It is
more plentiful than any other substance in rocks and in the clays and
ordinary soils, which are the finely ground particles of rock material.

_Iron_ is one of the commonest of elements. We know it by its red
colour. A rusty nail is covered with oxide of iron, a combination which
is readily formed wherever iron is exposed to the action of water or
air. You have seen yellowish or red streaks in clefts of the rocks. This
shows where water has dissolved out the iron and formed the oxide. The
red colour of New Jersey soil is due to the iron it contains. Indeed,
the whole earth's crust is rich in iron which the water easily
dissolves. The roots of plants take up quantities of iron in solution
and this mounts to the blossoms, leaves, and fruit. The red or yellow
colour of autumn leaves, of apples, of strawberries, of tulips, and of
roses, is produced by iron. The rosy cheeks of children are due to iron
in the food they eat and in the water they drink. The doctor but follows
the suggestion of nature when he gives a pale and listless person a
tonic of iron to make his blood red.

Iron is rarely found free, but it forms about five per cent. of the
crust of the earth, and it is believed to form at least one-fifth of the
unknown centre of the earth, the bulk of the globe, the weight of which
we know, but concerning the substance of which we can say little that is
positive.

_Manganese_ is not a conspicuous element, but is found united with
oxygen in purplish or black streaks on the sides of rocks. It is
somewhat like iron, but much less common.

_Calcium_ is the element that is the foundation of limestones. The
skeletons and shells of animals are made of calcite, a common mineral
formed by the uniting of carbon, oxygen, and calcium. Marbles are,
perhaps, the most permanent form of the limestone rocks. "Hard" water
has filtered through rocks containing calcite, and absorbed particles of
this mineral. From water thus impregnated, all animal life on the earth
obtains its bone-building and shell-building materials.

_Carbon_ forms a large part of the tissues of plants and animals, and in
the remains of these it is chiefly found in the earth's crust. When
these burn or decay, the carbon remains as charcoal or escapes to the
air in union with oxygen as the well known carbonic acid gas. This is
one of the most important foods of plants. Joined with calcium it forms
the mineral calcite, or carbonate of lime.

_Hydrogen_ is one of the two gases that unite to form water. Oxygen is
the other. Many kinds of rock contain a considerable amount of water.
Surface water sinks into porous soils and rocks, and accumulates in
pockets and veins which feed springs, and are the reserve water supply
that keeps our rivers flowing, even through dry weather. More water is
held by absorption in the earth's solid crust than in all the oceans and
seas and great lakes.

Hydrogen, combined with carbon, occurs in solid rocks where the remains
of plants and animals have slowly decayed. From such processes the
so-called hydrocarbons, rock oil and natural gas, have accumulated. When
such decay goes on above ground, these valuable products escape into the
air. Marsh gas, whose feeble flame above decaying vegetation is the
will-o'-the-wisp of swamps, is an example.

_Magnesium_, _potassium_, and _sodium_ are found in equal quantities in
the earth's crust, but never free. In union with chlorine, each forms a
soluble salt, and is thus found in water. Common salt, chloride of
sodium, is the most abundant of these. Water dissolves salt out of the
rocks, and carries it into the sea. Clouds that rise by the evaporation
of ocean water leave the salt behind, hence the seas are becoming more
and more salty, for the rivers carry salt to the oceans, which hold fast
all they get.

_Phosphorus_ is an element found united with oxygen in the tissues of
both plants and animals. It is most abundant in bones. Rocks containing
fossil bones are rich in lime phosphates, which are important commercial
fertilizers for enriching the soil. Beds of these rocks are found and
mined in South Carolina and elsewhere.

_Sulphur_ is well known as a yellow powder found most plentifully in
rocks that are near volcanoes. It is a needed element in plant and
animal bodies. It occurs in rocks, united with many different elements.
In union with oxygen and a metal it forms the group of minerals called
sulphates. In union with iron it forms sulphide of iron. The "fool's
gold" which Captain John Smith's colonists found in the sand at
Jamestown, was this worthless iron pyrites.

_Chlorine_ is a greenish, yellow gas, very heavy, and dangerous to
inhale. If it gets into the lungs, it settles into the lowest levels,
and one must stand on one's head to get it out. As an element of the
earth's crust it is not very plentiful, but it is a part of all the
chlorides of sodium, magnesium, and potassium. In salt, it forms two per
cent. of the sea water. It is much less abundant in the rocks.

To these elements we might add _nitrogen_, that invisible gas which
forms nearly four-fifths of our atmosphere, and is a most important
element of plant food in the soil. Most of the seventy elements are very
rare. Many are metals, like gold and iron and silver. Some are not
metals. Some are solid. A few are liquid, like the metal mercury, and
several are gaseous. Some are free and pure, and show no disposition to
unite with others. Nuggets of gold are examples of this. Some exist only
in union with other elements. This is the common rule among the
elements. Changes are constantly going on. The elements are constantly
abandoning old partnerships and forming new ones. Growth and decay of
plant and animal life are but parts of the great programme of constant
change which is going on and has been in progress since the world
began.

THE FIRST DRY LAND

When the earth's crust first formed it was still hot, though not so hot
as when it was a mass of melted, glowing substance. As it moved through
the cold spaces of the sky, it lost more heat and its crust became
thicker. At length the cloud masses became condensed enough to fall in
torrents of water, and a great sea covered all the land. This was before
any living thing, plant or animal, existed on our planet. Can you
imagine the continents and islands that form the land part of a map or
globe suddenly overwhelmed by the oceans, the names and boundaries of
which you have taken such pains to learn in the study of geography? The
globe would be one blank of blue water, and geography would be
abolished--and there would be nobody to study it. Possibly the fishes in
the sea might not notice any change in the course of their lives, except
when they swam among the ruins of buried cities and peered into the
windows of high buildings, or wondered what new kind of seaweed it was
when they came upon a submerged forest.

In that old time of the great sea that covered the globe, we are told
that there was a dense atmosphere over the face of the deep. So things
were shaping themselves for the far-off time when life should exist,
not only in the sea, where the first life did appear, but on land. But
it took millions of years to fit the earth for living things.

The cooling of the earth made it shrink, and the crust began to be
folded into gentle curves, as the skin of a shrunken apple becomes
wrinkled on the flesh. Some of these creases merely changed the depth of
water on the sea bottom; but one ridge was lifted above the water. The
water parted and streamed down its sloping sides, and a granite reef,
which shone in the sunshine, became the first dry land. It lay east and
west, and stretched for many miles. It is still dry land and is a part
of our own continent. Now it is but a small part of the country, but it
is known by geologists, who can tell its boundaries, though newer land
joins it on every side. It is named the Laurentian Hills, on geological
maps. Its southern border reaches along the northern boundary of the
Great Lakes to the head-waters of the Mississippi River.

From this base, two ridges are lifted, forming a colossal V. One extends
northeast to Nova Scotia; the other northwest to the Arctic seas. The V
encloses Hudson Bay.

Besides this first elongated island of bare rocks, land appeared in a
strip where now the Blue Ridge Mountains stretch from New England to
Georgia. The other side of the continent lifted up two folds of the
crust above sea level. They are the main ridges of the Colorado and the
Wasatch Mountains. Possibly the main ridge of the Sierra Nevada rose
also at this time. The Ozark group of mountains, too, showed as a few
island peaks above the sea.

These first rocks were rapidly eaten away, for the atmosphere was not
like ours, but heavily charged with destructive gases, which did more,
we believe, to disintegrate the exposed rock surfaces than did the two
other forces, wind and water, combined. The sediment washed down to the
sea by rains, accumulated along the shores, filling the shallows and
thus adding to the width of the land areas. The ancient granite ridge of
the Laurentian Hills is now low, and slopes gently. This is true of all
very old mountains. The newer ones are high and steep. It takes time to
grind down the peaks and carry off the waste material loosened by
erosion.

Far more material than could have been washed down the slopes of the
first land ridges came directly from the interior of the earth, and
spread out in vast, submarine layers upon the early crust. Volcanic
craters opened under water, and poured out liquid mineral matter, that
flowed over the sea bottom before it cooled. Imagine the commotion that
agitated the water as these submerged chimneys blew off their lids, and
discharged their fiery contents! It was long before the sea was cool
enough to be the home of living things.

The layers of rock that formed under the sea during this period of the
earth's history are of enormous thickness. They were four or five miles
deep along the Laurentian Hills. They broadened the original granite
ridge by filling the sea bottom along the shores. The backbones of the
Appalachian system and the Cordilleras were built up in the same
way--the oldest rocks were worn away, and their débris built up newer
ones in strata.

When these layers of rock became dry land, the earth's crust was much
more stable and cool than it had ever been before. The vast
rock-building of that era equals all that has been done since. The
layers of rocks formed since then do not equal the total thickness of
these first strata. So we believe that the time required to build those
Archæan rock foundations equals or surpasses the vast period that has
elapsed since the Archæan strata were formed.

The northern part of North America has grown around those old granite
ridges by the gradual rising of the shores. The geologist may walk along
the Laurentian Hills, that parted the waters into a northern and a
southern ocean. He crosses the rocky beds deposited upon the granite;
then the successive beds formed as the land rose and the ocean receded.
Age after age is recorded in the rocks. Gradually the sea is crowded
back, and the land masses, east, west, and north, meet to form the
continent. Nowhere on the earth are the steps of continental growth
shown in unbroken sequence as they are in North America.

How long ago did those first islands appear above the sea? Nobody
ventures a definite answer to this question. No one has the means of
knowing. But those who know most about it estimate that at the least one
hundred million years have passed since then--one hundred thousand
thousand years!

A STUDY OF GRANITE

In Every village cemetery it is easy to find shafts of gray or speckled
granite, the polished surfaces of which show that the granite is made of
small bits of different coloured minerals, cemented together into solid
rock. Outside the gate you will usually find a place where monuments and
gravestones may be bought. Here there is usually a stonecutter chipping
away on a block with his graving tools. He is a man worth knowing, and
because his work is rather monotonous he will probably be glad to talk
to a chance visitor and answer questions about the different kinds of
stone on which he works.

There are bits of granite lying about on the ground. If you have a
hand-glass of low power, such as the botany class uses to examine the
parts of flowers, it will be interesting to look through it and see the
magnified surface of a flake of broken granite. Here are bits of glassy
quartz, clear and sparkling in the sun. Black and white may be all the
colours you make out in this specimen, or it may be that you see specks
of pink, dark green, gray, and smoky brown, all cemented together with
no spaces that are not filled. The particles of quartz are of various
colours, and are very hard. They scratch glass, and you cannot scratch
them with the steel point of your knife, as you can scratch the other
minerals associated with the grains of quartz.

Granite is made of quartz, feldspar, and mica, sometimes with added
particles of hornblende. Feldspar particles have as wide a range of
colour as quartz, but it is easy to tell the two apart. A knife will
scratch feldspar, as it is not so hard as quartz. The crystals of
feldspar have smooth faces, while quartz breaks with a rough surface as
glass does. Feldspar loses its glassy lustre when exposed to the
weather, and becomes dull, with the soft lustre of pearl.

Mica may be clear and glassy, and it ranges in colour from transparency
through various shades of brown to black. It has the peculiarity of
splitting into thin, leaf-like, flexible sheets, so it is easy to find
out which particles in a piece of granite are mica. One has only to use
one's pocket knife with a little care. Hornblende is a dark mineral
which contains considerable iron. It is found in lavas and granites,
where it easily decays by the rusting of the iron. It is not unusual to
see a rough granite boulder streaked with dark red rust from this cause.

The crumbling of granite is constantly going on as a result of the
exposure of its four mineral elements to the air. Quartz is the most
stable and resistant to weathering. Soil water trickling over a granite
cliff has little effect on the quartz particles; but it dissolves out
some of the silicon. The bits of feldspar are even more resistant to
water than quartz is, but the air causes them to decay rapidly, and
finally to fall away in a sort of mealy clay. Mica, like feldspar,
decays easily. Its substance is dissolved by water and carried away to
become a kind of clay. The hornblende rusts away chiefly under the
influence of moist air and trickling water.

We think of granite as a firm, imperishable kind of rock, and use it in
great buildings like churches and cathedrals that are to stand for
centuries. But the faces that are exposed to the air suffer, especially
in regions having a moist climate. The signs of decay are plainly
visible on the outer surfaces of these stones. Fortunate it is that the
weathering process cannot go very deep.

The glassy polish on a smooth granite shaft is the silicon which acts as
a cement to bind all the particles together. It is resistant to the
weather. A polished shaft will last longer than an unpolished one.

Granites differ in colouring because the minerals that compose them, the
feldspars, quartzes, micas, and hornblendes, have each so wide a range
of colour. Again, the proportions of the different mineral elements vary
greatly in different granites. A banded granite the colours of which
give it a stratified appearance is called a gneiss.

We have spoken before of the seventy elements found in the earth's
crust. A mineral is a union of two or more of these different elements;
and we have found four minerals composing our granite rock. It may be
interesting to go back and inquire what elements compose these four
minerals. Quartz is made of silicon and oxygen. Feldspar is made of
silicon, oxygen, and aluminum. Mica is made of silicon, oxygen, and
carbon, with some mingling of potassium and iron and other elements in
differing proportions. Hornblende is made of silicon, oxygen, carbon,
and iron.

The crumbling of a granite rock separates the minerals that compose it,
reducing some to the condition of clay, others to grains of sand. Some
of the elements let go their union and become free to form new unions.
Water and wind gather up the fragments of crumbling granite and carry
them away. The feldspar and mica fragments form clay; the quartz
fragments, sand. All of the sandstones and slates, the sand-banks and
sand beaches, are made out of crumbled granite, the rocky foundations of
the earth.

METAMORPHIC ROCKS

In the dawn of life on the earth, soft-bodied creatures, lowest in the
scale of being, inhabited the sea. The ancient volcanoes the
subterranean eruptions of which had spread layers of mineral substance
on the ocean floor, and heated the water to a high degree, had subsided.
The ocean was sufficiently cool to maintain life. The land was being
worn down, and its débris washed into the ocean. The first sand-banks
were accumulating along sandy shores. The finer sediment was carried
farther out and deposited as mud-banks. These were buried under later
deposits, and finally, by the rising of the earth's crust, they became
dry land. Time and pressure converted the sand-banks into sandstones;
the mud-banks into clay. The remains of living creatures utterly
disappeared, for they had no hard parts to be preserved as fossils.

The shrinking of the earth's crust had crumpled into folds of the utmost
complexity those horizontal layers of lava rock poured out on the ocean
floor. Next, the same forces attacked the thick rock layers formed out
of sediment--the aqueous or water-formed sandstones and clays.

The core of the globe contracts, and the force that crumples the crust
to fit the core generates heat. The alkaline water in the rocks joins
with the heat produced by the crumpling and crushing forces, acting
downward, and from the sides, to transform pure sandstone into glassy
quartzite, and clay into slate. In other words, water-formed rocks are
baked until they become fire-formed rocks. They are what the geologist
calls _metamorphic_, which means _changed_.

In many mountainous regions there are breaks through the strata of
sandstone and slates and limestones, through which streams of lava have
poured forth from the heated interior. Along the sides of these fissures
the hot lava has changed all the rocks it touched. The heat of the
volcanic rock matter has melted the silica in the sand, which has
hardened again into a crystalline substance like glass.

Have you ever visited a brick-yard? Here men are sifting clay dug out of
a pit or the side of a hill, adding sand from a sand-bank, and in a big
mixing box, stirring these two "dry ingredients" with water into a thick
paste. This dough is moulded into bricks, sun-dried, and then baked in
kilns themselves built of bricks. At the end of the baking, the soft,
doughy clay block is transformed into a hard, glassy, or dull brick.
From aqueous rock materials, fire has produced a metamorphic rock.
Volcanic action is imitated in this common, simple process of
brickmaking.

Milwaukee brick is made of clay that has no iron in it. For this reason
the bricks are yellow after baking. Most bricks are red, on account of
the iron in the clay, which is converted into a red oxide, or rust, by
water and heat.

Common flower pots and the tiles used in draining wet land are not
glazed, as hard-burned bricks are. The baking of these clay things is
done with much less heat. They are left somewhat porous. But the tiles
of roofs are baked harder, and get a surface glaze by the melting of the
glassy particles of the sand.

As bricks vary in colour and quality according to the materials that
compose them, so the metamorphic rocks differ. The white sand one sees
on many beaches is largely quartz. This is the substance of pure, white
sandstone. Metamorphism melts the silica into a glassy liquid cement;
the particles are bound close together on cooling. The rock becomes a
white, granular quartzite, that looks like loaf sugar. If banded, it is
called gneiss. Such rocks take a fine polish.

Pure limestone is also white and granular. When metamorphosed by heat,
it becomes white marble. The glassy cement that holds the particles of
lime carbonate shows as the glaze of the polished surface. It is silica.
One sees the same mineral on the face of polished granite.

Clays are rarely pure. Kaolin is a white clay which, when baked, becomes
porcelain. China-ware is artificially metamorphosed kaolin. In the
early rocks the clay beds were transformed by heat into jasper and
slates. In beds where clay mingled with sand, in layers, gneiss was
formed. If mica is a prominent element, the metamorphic rock is easily
parted into overlapping, scaly layers. It is a mica schist. If
hornblende is the most abundant mineral, the same scaly structure shows
in a dark rock called hornblende schist, rich in iron. A schist
containing much magnesia is called serpentine.

The bricks of the wall, the tiles on the roof, the flower pots on the
window sill, and the dishes on the breakfast table, are examples of
metamorphic rocks made by man's skill, by the use of fire and water
acting on sand and clay. Pottery has preserved the record of
civilization, from the making of the first crude utensils by cave men to
the finest expression of decorative art in glass and porcelain.

The choicest material of the builder and the sculptor is limestone baked
by the fires under the earth's crust into marble. The most enduring of
all the rocks are the foundation granite, and the metamorphic rocks that
lie next to them. Over these lie thick layers of sedimentary rocks laid
down by water. In them the record of life on the earth is written in
fossils.

THE AIR IN MOTION

Most of the beautiful things that surround us and make our lives full of
happiness appeal to one or more of our five senses. The green trees we
can see, the bird songs we hear, the perfume of honey-laden flowers we
smell, the velvety smoothness of a peach we feel, and its rich pulp we
taste. But over all and through all the things we see and feel and hear
and taste and smell, is the life-giving air, that lies like a blanket,
miles in depth, upon the earth. The substance which makes the life of
plants and animals possible is, when motionless, an invisible,
tasteless, odourless substance, which makes no sound and is not
perceptible to the touch.

Air fills the porous substance of the earth's crust for a considerable
distance, and even the water has so much air in it that fishes are able
to breathe without coming to the surface. It is not a simple element,
like gold, or carbon, or calcium, but is made up of several elements,
chief among which are nitrogen and oxygen. Four-fifths of its bulk is
nitrogen and one-fifth oxygen. There is present in air more or less of
watery vapour and of carbon dioxide, the gas which results from the
burning or decay of any substance. Although no more than one per cent.
of the air that surrounds us is water, yet this is a most important
element. It forms the clouds that bear water back from the ocean and
scatter it in rain upon the thirsty land. Solid matter in the form of
dust, and soot from chimneys, accumulates in the clouds and does a good
work in condensing the moisture and causing it to fall.

It is believed that the air reaches to a height of one hundred to two
hundred miles above the earth's surface. If a globe six feet in diameter
were furnished with an atmosphere proportionately as deep as ours, it
would be about an inch in depth. At the level of the sea the air reaches
its greatest density. Two miles above sea-level it is only two-thirds as
dense. On the tops of high mountains, four or five miles above sea
level, the air is so rarefied as to cause the blood to start from the
nostrils and eyelids of explorers. The walls of the little blood-vessels
are broken by the expansion of the air that is inside. At the sea-level
air presses at the rate of fifteen pounds per square foot in all
directions. As one ascends to higher levels, the air pressure becomes
less and less.

The barometer is the instrument by which the pressure of air is
measured. A glass tube, closed at one end, and filled with mercury, the
liquid metal often called quicksilver, is inverted in a cup of the same
metal, and so supported that the metal is free to flow between the two
vessels. The pressure of air on the surface of the mercury in the cup is
sufficient at the sea-level to sustain a column of mercury thirty
inches high in the tube. As the instrument is carried up the side of a
mountain the mercury falls in the tube. This is because the air pressure
decreases the higher up we go. If we should descend into the shaft of
the deepest mine that reaches below the sea level, the column of air
supported by the mercury in the cup would be a mile higher, and for this
reason its weight would be correspondingly greater. The mercury would
thus be forced higher in the tube than the thirty-inch mark, which
indicates sea-level.

Another form of barometer often seen is a tube, the lower and open end
of which forms a U-shaped curve. In this open end the downward pressure
of the air rests upon the mercury and holds it up in the closed end,
forcing it higher as the instrument is carried to loftier altitudes. At
sea level a change of 900 feet in altitude makes a change of an inch in
the height of the mercury in the column. The glass tube is marked with
the fractions of inches, or of the metre if the metric system of
measurements is used.

It is a peculiarity of air to become heated when it is compressed, and
cooled when it is allowed to expand again. It is also true that when the
sun rises, the atmosphere is warmed by its rays. This is why the hottest
part of the day is near noon when the sun's rays fall vertically. The
earth absorbs a great deal of the sun's heat in the daytime and through
the summer season. When it cools this heat is given off, thus warming
the surrounding atmosphere. In the polar regions, north and south, the
air is far below freezing point the year round. In the region of the
Equator it rarely falls below 90 degrees, a temperature which we find
very uncomfortable, especially when there is a good deal of moisture in
the air.

If we climb a mountain in Mexico, we leave the sultry valley, where the
heat is almost unbearable, and very soon notice a change. For every
three hundred feet of altitude we gain there is a fall of one degree in
the temperature. Before we are half way up the slope we have left behind
the tropical vegetation, and come into a temperate zone, where the
plants are entirely different from those in the lower valley. As we
climb, the vegetation becomes stunted, and the thermometer drops still
lower. At last we come to the region of perpetual snow, where the
climate is like that of the frozen north.

So we see that the air becomes gradually colder as we go north or south
from the Equator, and the same change is met as we rise higher and
higher from the level of the sea.

It is only when air is in motion that we can feel and hear it, and there
are very few moments of the day, and days of the year, when there is not
a breeze. On a still day fanning sets the air in motion, and creates a
miniature breeze, the sound of which we hear in the swishing of the fan.
The great blanket of air that covers the earth is in a state of almost
constant disturbance, because of the lightness of warm air and the
heaviness of cold air. These two different bodies are constantly
changing places. For instance, the heated air at the Equator is
constantly being crowded upward by cold air which settles to the level
of the earth. Cold streams of air flow to the Tropics from north and
south of the Equator, and push upward the air heated by the sun.

This constant inrush of air from north and south forms a double belt of
constant winds. If the earth stood still, no doubt the direction would
be due north and due south for these winds; but the earth rotates
rapidly from west to east upon its axis, carrying with it everything
that is securely fastened to the surface: the trees, the houses, etc.
But the air is not a part of the earth, not even so much as the seas,
the waters of which must stay in their proper basins, and be whirled
around with other fixed objects. The earth whirls so rapidly that the
winds from north and south of the Equator lag behind, and thus take a
constantly diagonal direction. Instead of due south the northern belt of
cold air drifts south-west and the southern belt drifts northwest. These
are called the Trade Winds. Near the Equator they are practically east
winds.

The belt of trade winds is about fifty degrees wide. It swings northward
in our summer and southward in our winter, its centre following the
vertical position of the sun. Near the centre of the course which marks
the meeting of the northern with the southern winds is a "Belt of
Calms" where the air draws upward in a strong draught. The colder air of
the trade winds is pushing up the columns of light, heated air. This
strip is known by sailors as "the Doldrums," or "the region of
equatorial calms." Though never wider than two or three hundred miles,
this is a region dreaded by captains of sailing-vessels, for they often
lie becalmed for weeks in an effort to reach the friendly trade winds
that help them to their desired ports. Vessels becalmed are at the mercy
of sudden tempests which come suddenly like thunder-storms, and
sometimes do great damage to vessels because they take the sailors
unawares and allow no time to shorten sail.

Until late years the routes of vessels were charted so that sailors
could take advantage of the trade winds in their long voyages. It was
necessary in the days of sailing-vessels for the captain to understand
the movements of winds which furnished the motive power that carried his
vessel. Fortunate it was for him that there were steady winds in the
temperate zones that he could take advantage of in latitudes north of
the Tropic of Cancer and south of the Tropic of Capricorn. What becomes
of the hot air that rises in a constant stream above the "Doldrums,"
pushed up by the cooler trade winds that blow in from north and south?
Naturally this air cannot ascend very high, for it soon reaches an
altitude in which its heat is rapidly lost, and it would sink if it
were not constantly being pushed by the rising column of warm air under
it. So it turns and flows north and south at a level above the trade
winds. Not far north of the Tropic of Cancer it sinks to the level of
sea and land, and forms a belt of winds that blows ships in a
northeasterly direction. Between trades and anti-trades is another zone
of calms,--near the Tropics of Cancer and of Capricorn.

The land masses of the continents with their high mountain ranges
interfere with these winds, especially in the northern hemisphere, but
in the Southern Pacific and on the opposite side of the globe the
"Roaring Forties," as these prevailing westerly winds are known by the
sailors, have an almost unbroken waste of seas over which they blow. In
the long voyages between England and Australia, and in the Indian trade,
the ships of England set their sails to catch the roaring forties both
going and coming. They accomplish this by sailing past the Cape of Good
Hope on the outward voyage and coming home by way of Cape Horn, thus
circling the globe with every trip. In the North Atlantic, traffic is
now mostly carried on in vessels driven by engines, not by sails. Yet
the westerly winds that blow from the West Indies diagonally across the
Atlantic are still useful to all sailing craft that are making for
British ports.

From the north and from the south cold air flows down into the regions
of warmer climate. These polar winds are not so important to sea
commerce, but they do a great work in tempering the heat in the
equatorial regions. We cannot know how much our summers are tempered by
the cool breath of winds that blow over polar ice-fields. And the cold
regions of the earth, in their brief summer, enjoy the benefits of the
warm breezes that flow north and south from the heated equatorial
regions.

The land, north and south, is made habitable by the clouds. They gather
their burdens of vapour from the warm seas, the wind drifts them north
and south, where they let it fall in rains that make and keep the earth
green and beautiful. From the clouds the earth gathers, like a great
sponge, the water that stores the springs and feeds rivers and lakes.
How necessary are the winds that transport the cloud masses!

The air is the breath of life to all living things on our planet. Mars
is one of the sun's family so provided. Plants or animals could probably
live on the planet Mars. Do we think often enough of this invisible,
life-giving element upon which we depend so constantly?

The open air which the wind purifies by keeping it in motion is the best
place in which to work, to play, and to sleep, when work and play are
done and we rest until another day comes. Indoors we need all the air we
can coax to come in through windows and doors. Fresh air purifies air
that is stale and unwholesome from being shut up. Nobody is afraid,
nowadays, to breathe night air! What a foolish notion it was that led
people to close their bedroom windows at night. Clean air, in plenty,
day and night, we need. Air and sunshine are the two best gifts of God.

THE WORK OF THE WIND

When the March wind comes blustering down the street, rudely dashing a
cloud of dust in our faces, we are uncomfortable and out of patience. We
duck our heads and cover our faces, but even then we are likely to get a
cinder in one eye, to swallow germs by the dozens, and to get a gray
coating of plain, harmless dust. We welcome the rain that lays the dust,
or its feeble imitation, the water sprinkler, that brings us temporary
relief.

On the quietest day, even after a thorough sweeping and dusting of the
library, you are able to write your name plainly on the film of dust
that lies on the polished table. Take a book from the open shelves, and
blow into the trough of its top. This is always dusty. Where does the
dust come from? This is the house-keeper's riddle.

The answer is not a hard one. I look out of my window on a street which
is famous as the road Washington took on his retreat from White Plains
to Trenton. It has always been the main thoroughfare between New York
and Philadelphia, and now is the route that automobiles follow. A
constant procession of vehicles passes my house, and to-day each one
approaches in a cloud of dust. The air is gray with suspended particles
of dirt. The wind carries the successive clouds, and they roll up
against the houses like breakers on the beach. Windows and doors are
loose enough to let dust sift in. When a door opens, the cloud enters
and lights on rugs and carpets and curtains. Any ledge collects its
share of dust. The beating of carpets and rugs disturbs the accumulated
dust of many months.

[Illustration: In this lonely Arizona desert the wind drifts the sand
into dunes, just as it does on the toe of Cape Cod]

[Illustration: The Grand Canyon of the Colorado shows on a magnificent
scale the work of water in cutting away rock walls]

The wind sweeps the ploughed field, and takes all the dust it can carry.
It blows the finest top soil from our gardens into the street. It blows
soil from other fields and gardens into ours, so the level of our land
is not noticeably lowered. The wind strips the high land and drops its
burden on lower levels. This is one of the big jobs the water has to do,
and the wind is a valuable helper. To tear down the mountains and fill
in the valleys is the great work of the two partners, wind and water.

Dead, still air holds the finest dust, without letting it fall. The
buoyancy of the particles overcomes their weight. We see them in a
sunbeam, like shining points of precious metal, and watch them. A light
breeze picks up bits of soil and litter, from the smallest up to a
certain size and weight. If the velocity of the wind increases, its
carrying power increases. It is able to carry bits that are larger and
heavier. The following table is exact and interesting:

_Velocity_ _Pressure_
_in Miles_ _in Pounds_
_per Hour_ _per Sq. Ft._

Light breeze 14 1
Strong breeze 42 9
Strong gale 70 25
Hurricane 84 36

The terrible paths of hurricanes are seen in forest countries. The trees
are uprooted, as if a great roller had crushed them, throwing the tops
all in one direction, and leaving the roots uncovered, and a sunken
pocket where each tree stood. On a steep, rocky slope, the uprooting of
scattered trees often loosens tons of rock, and sends the mass
thundering down the mountain-side. Much more destruction may be
accomplished by one brief tornado than by years of wear by ordinary
breezes.

The wind does much to help the waves in their patient beating on rocky
shores. If the wind blows from the ocean and the tide is landward, the
two forces combine, and the loose rocks are thrown against the solid
beach with astonishing force. Even the gravel and the sharp sand are
tools of great usefulness to the waves in grinding down the resisting
shore. Up and back they are swept by the water, and going and coming
they have their chance to scratch or strike a blow. Boulders on the
beach become pockmarked by the constant sand-blast that plays upon them.
The lower windows of exposed seaside houses are dimmed by the sand that
picks away the smooth surface outside, making it ground glass by the
same process used in the factory. Lighthouses have this difficulty in
keeping their windows clear. The "lantern" itself is sometimes reached
by the sand grains. That is the cupola in which burns the great light
that warns vessels away from the rocks and tells the captain where he
is.

In the Far Western States the telegraph poles and fence posts are soon
cut off at the ground by the flinty knives the wind carries. These are
the grains of sand that are blown along just above the ground. The trees
are killed by having their bark girdled in this way. The sand-storms
which in the orange and lemon region of California are called "Santa
Anas" sometimes last two or three days, and damage the trees by piercing
the tender bark with the needle-pointed sand.

Wind-driven soil, gathered from the sides of bare hills and mountains,
fills many valleys of China with a fine, hard-packed material called
"loess." In some places it is hundreds of feet deep. The people dig into
the side of a hill of this loess and carry out the diggings, making
themselves homes, of many rooms, with windows, doors, and solid walls
and floors, all in one solid piece, like the chambered house a mole
makes underground in the middle of a field. So compact is the loess that
there is no danger of a cave-in.

The hills of sand piled up on the southern shore of Lake Michigan, and
at Provincetown, at the toe of Cape Cod, are the work of the wind. On
almost any sandy shore these "dunes" are common. The long slope is
toward the beach that furnishes the sand. The wind does the building. Up
the slope it climbs, then drops its burden, which slides to the bottom
of an abrupt landward steep. There is a gradual movement inland if the
strongest winds come from the water. The shifting of the dunes threatens
to cover fertile land near them. In the desert regions, the border-land
is always in danger of being taken back again, even though it has been
reclaimed from the desert and cultivated for long years.

Besides tearing down, carrying away, and building up again the fragments
of the earth's crust, the wind does much that makes the earth a pleasant
planet to live on. It drives the clouds over the land, bringing rains
and snows and scattering them where they will bless the thirsty ground
and feed the springs and brooks and rivers. It scatters the seeds of
plants, and thus plants forests and prairies and lovely mountain slopes,
making the wonderful wild gardens that men find when they first enter
and explore a new region. The trade winds blow the warm air of the
Tropics north and south, making the climate of the northern countries
milder than it would otherwise be. Sea winds blow coolness over the land
in summer, and cool lake breezes temper the inland regions. From the
snow-capped mountains come the winds that refresh the hot, tired worker
in the valleys.

Everywhere the wind blows, the life-giving oxygen is carried. This is
what we mean when we speak of fresh air. Stagnant air is as unwholesome
as stagnant water. Constant moving purifies both. So we must give the
wind credit for some of the greatest blessings that come into our lives.
Light and warmth come from the sun. Pure water and pure air are gifts
the bountiful earth provides. Without them there would be no life on the
earth.

RAIN IN SUMMER

How beautiful is the rain!
After the dust and heat,
In the broad and fiery street,
In the narrow lane,
How beautiful is the rain!

How it clatters along roofs,
Like the tramp of hoofs!
How it gushes and struggles out
From the throat of the overflowing spout!
Across the window-pane

It pours and pours;
And swift and wide,
With a muddy tide,
Like a river down the gutter roars
The rain, the welcome rain!

The sick man from his chamber looks
At the twisted brooks;
He can feel the cool
Breath of each little pool;
His fevered brain
Grows calm again,
And he breathes a blessing on the rain.

--HENRY W. LONGFELLOW.

WHAT BECOMES OF THE RAIN?

The clouds that sail overhead are made of watery vapour. Sometimes they
look like great masses of cotton-wool against the intense blue of the
sky. Sometimes they are set like fleecy plumes high above the earth.
Sometimes they hang like a sullen blanket of gray smoke, so low they
almost touch the roofs of the houses. Indeed, they often rest on the
ground and then we walk through a dense fog.

In their various forms, clouds are like wet sponges, and when they are
wrung dry they disappear--all their moisture falls upon the earth. When
the air is warm, the water comes in the form of rain. If it is cold, the
drops are frozen into hail, sleet, or snow.

All of the water in the oceans, in the lakes and rivers, great and
small, all over the earth, comes from one source, the clouds. In the
course of a year enough rain and snow fall to cover the entire surface
of the globe to a depth of forty inches. This quantity of water amounts
to 34,480 barrels on every acre. What becomes of it all?

We can easily understand that all the seas and the other bodies of water
would simply add forty inches to their depth, and many would become
larger, because the water would creep up on their gradually sloping
shores. We have to account for the rain and the snow that fall upon the
dry land and disappear.

Go out after a drenching rainstorm and look for the answer to this
question. The gullies along the street are full of muddy, running water.
There are pools of standing water on level places, but on every slope
the water is hurrying away. The ground is so sticky that wagons on
country roads may mire to the hubs in the pasty earth. There is no use
in trying to work in the garden or to mow the lawn. The sod is soft as a
cushion, and the garden soil is water-soaked below the depth of a
spading-fork.

The sun comes out, warm and bright, and the flagstones of the sidewalk
soon begin to steam like the wooden planks of the board walk. The sun is
changing the surface water into steam which rises into the sky to form a
part of another bank of clouds. The earth has soaked up quantities of
the water that fell. If we followed the racing currents in the gullies
we should find them pouring into sewer mains at various points, and from
these underground pipes the water is conducted to some outlet like a
river. All of the streams are swollen by the hundreds of brooks and
rivulets that are carrying the surface water to the lowest level.

[Illustration: Rain and wind are the sculptors that have carved these
strange castles out of a rocky table]

[Illustration: All the water in the seas, lakes, rivers, and springs
came out of the clouds]

So we can see some of the rainfall going back to the sky, some running
off through rivulets to the sea, and some soaking into the ground. It
will be interesting to follow this last portion as it gradually settles
into the earth. The soil will hold a certain quantity, for it is made up
of fine particles, all separated by air spaces, and it acts like a
sponge. In seasons of drought and great heat the sun will draw this soil
water back to the surface, by forming cracks in the earth, and fine,
hair-like tubes, through which the vapour may easily rise. The gardener
has to rake the surface of the beds frequently to stop up these channels
by which the sun is stealing the precious moisture.

The water that the surface soil cannot absorb sinks lower and lower into
the ground. It finds no trouble to settle through layers of sand, for
the particles do not fit closely together. It may come to a bed of clay
which is far closer. Here progress is retarded. The water may
accumulate, but finally it will get through, if the clay is not too
closely packed. Again it may sink rapidly through thick beds of gravel
or sand. Reaching another bed of clay which is stiffer by reason of the
weight of the earth above it, the water may find that it cannot soak
through. The only way to pass this clay barrier is to fill the basin,
and to trickle over the edge, unless a place is found in the bottom
where some looser substance offers a passage. Let us suppose that a
concave clay basin of considerable depth is filled with water-soaked
sand. At the very lowest point on the edge of this basin a stream will
slowly trickle out, and will continue to flow, as long as water from
above keeps the bowl full.

It is not uncommon to find on hillsides, in many regions, little brooks
whose beginnings are traceable to springs that gush out of the ground.
The spring fills a little basin, the overflow of which is the brook. If
the source of this spring could be traced underground, we might easily
follow it along some loose rock formation until we come to a clay basin
like the one described above. We might have to go down quite a distance
and then up again to reach the level of this supply, but the level of
the water at the mouth of the spring can never be higher than the level
of the water in the underground supply basin.

Often in hot summers springs "go dry." The level of water in the supply
basin has fallen below the level of the spring. We must wait until
rainfall has added to the depth of water in the basin before we can
expect any flow into the pool which marks the place where the brook
begins.

Suppose we had no beds of clay, but only sand and gravel under the
surface soil. We should then expect the water to sink through this loose
material without hindrance, and, finding its way out of the ground, to
flow directly into the various branches of the main river system of our
region. After a long rain we should have the streams flooded for a few
days, then dry weather and the streams all low, many of them entirely
dry until the next rainstorm.

Instead of this, the soil to a great depth is stored with water which
cannot get away, except by the slow process by which the springs draw
it off. This explains the steady flow of rivers. What should we do for
wells if it were not for the water basins that lie below the surface? A
shallow well may go dry. Its owner digs deeper, and strikes a lower
"vein" of water that gives a more generous supply. In the regions of the
country where the drift soil, left by the great ice-sheet, lies deepest,
the glacial boulder clay is very far down. The surface water, settling
from one level to another, finally reaches the bottom of the drift.
Wells have to be deep that reach this water bed.

The water follows the slope of this bed and is drained into the ocean,
sometimes by subterranean channels, because the bed of the nearest river
is on a much higher level. So we must not think that the springs contain
only the water that feeds the rivers. They contain more.

The layers of clay at different levels, from the surface down to the
bottom of the drift, form water basins and make it possible for people
to obtain a water supply without the expense of digging deep wells. The
clayey subsoil, only a few feet below the surface, checks the downward
course of the water, so that the sun can gradually draw it back, and
keep a supply where plant roots can get it. The vapour rising keeps the
air humid, and furnishes the dew that keeps all plant life comfortable
and happy even through the hot summer months.

Under the drift lie layers of stratified rock, and under these are the
granites and other fire-formed rocks, the beginning of those rock masses
which form the solid bulk of the globe. We know little about the core of
the earth, but the granites that are exposed in mountain ridges are
found to have a great capacity for absorbing water, so it is not
unlikely that much surface water soaks into the rock foundations and is
never drained away into the sea.

The water in our wells is often hard. It becomes so by passing through
strata of soil and rock made, in part, at least, of limestone, which is
readily dissolved by water which contains some acid. Soil water absorbs
acids from the decaying vegetation,--the dead leaves and roots of
plants. Rain water is soft, and so is the water in ponds that have muddy
basins, destitute of lime. Water in the springs and wells of the
Mid-Western States is "hard" because it percolates through limestone
material. In many parts of this country the well water is "soft,"
because of the scarcity of limestone in the soil.

I have seen springs around which the plants and the pebbles were coated
with an incrustation of lime. "Petrified moss" is the name given to the
plants thus turned to stone. The reason for this deposit is clear.
Underground water is often subjected to great pressure, and at this time
it is able to dissolve much more of any mineral substance than under
ordinary conditions. When the pressure is released, the water is unable
to hold in solution the quantity of mineral it contains; therefore, as
it flows out through the mouth of the spring, the burden of mineral is
laid down. The plants coated with the lime gradually decay, but their
forms are preserved.

There are springs the water of which comes out burdened with iron, which
is deposited as a yellowish or red mineral on objects over which it
flows. Ponds fed by these springs accumulate deposits of the mineral in
the muddy bottoms. Some of the most valuable deposits of iron ore have
accumulated in bogs fed by iron-impregnated spring water. In a similar
way lime deposits called marl or chalk are made.

THE SOIL IN FIELDS AND GARDENS

City and country teachers are expected to teach classes about the
formation and cultivation of soil. It is surprising how much of the
needed materials can be brought in by the children, even in the cities.
The beginning is a flowering plant growing in a pot. A window box is a
small garden. A garden plot is a miniature farm.

_Materials to collect for study indoors._ A few pieces of different
kinds of rock: Granite, sandstone, slate; gravelly fragments of each,
and finer sand. Pebbles from brooks and seashore. Samples of clays of
different colors, and sands. Samples of sandy and clay soils, black pond
muck, peat and coal. Rock fossils. A box of moist earth with earthworms
in it. _Keep it moist._ A piece of sod, and a red clover plant with the
soil clinging to its roots.

_What is soil?_ It is the surface layer of the earth's crust, sometimes
too shallow on the rocks to plough, sometimes much deeper. Under deep
soil lies the "subsoil," usually hard and rarely ploughed.

_What is soil made of?_ Ground rock materials and decayed remains of
animal and plant life. By slow decay the soil becomes rich food for the
growing of new plants. Wild land grows up to weeds and finally to
forests. The soil in fields and gardens is cultivated to make it
fertile. Plants take fertility from the soil. To maintain the same
richness, plant food must be put back into the soil. This is done by
deep tillage, and by mixing in with the soil manures, green crops, like
clover, and commercial fertilizers.

_Plants must be made comfortable, and must be fed._ Few plants are
comfortable in sand. It gets hot, it lets water through, and it shifts
in wind and is a poor anchor for roots. Clay is so stiff that water
cannot easily permeate it; roots have the same trouble to penetrate it
and get at the food it is rich in. Air cannot get in.

Sand mixed with clay makes a mellow soil, which lets water and air pass
freely through. The roots are more comfortable, and the tiny root hairs
can reach the particles of both kinds of mineral food. But the needful
third element is decaying plant and animal substances, called "humus."
These enrich the soil, but they do a more important thing: their decay
hastens the release of plant food from the earthy part of the soil, and
they add to it a sticky element which has a wonderful power to attract
and hold the water that soaks into the earth.

_What is the best garden soil?_ A mixture of sand, clay, and humus is
called "loam." If sand predominates, it is a sandy loam--warm, mellow
soil. If clay predominates, we have a clay loam--a heavy, rich, but
cool soil. All gradations between the two extremes are suited to the
needs of crops, from the melons on sandy soil, to celery that prefers
deep, cool soil, and cranberries that demand muck--just old humus.

_How do plant roots feed in soil?_ By means of delicate root hairs which
come into contact with particles of soil around which a film of soil
water clings. This fluid dissolves the food, and the root absorbs the
fluid. Plants can take no food in solid form. Hence it is of the
greatest importance to have the soil pulverized and spongy, able to
absorb and hold the greatest amount of water. The moisture-coated soil
particles must have air-spaces between them. Air is as necessary to the
roots as to the tops of growing plants.

_Why does the farmer plough and harrow and roll the land?_ To pulverize
the soil; to mellow and lighten it; to mix in thoroughly the manure he
has spread on it, and to reach, if he can, the deeper layers that have
plant food which the roots of his crops have not yet touched. Killing
weeds is but a minor business, compared with tillage.

Later, ploughing or cultivating the surface lightly not only destroys
the weeds, but it checks the loss of water by evaporation from the
cracks that form in dry weather. Raking the garden once a day in dry
weather does more good than watering it. The "dust mulch" acts as a cool
sunguard over the roots.

_The process of soil-making._ If the man chopping wood in the Yosemite
Valley looks about him he can see the soil-making forces at work on a
grand scale. The bald, steep front of El Capitan is of the hardest
granite, but it is slowly crumbling, and its fragments are accumulating
at the bottom of the long slope. Rain and snow fill all crevices in the
rocks. Frost is a wonderful force in widening these cracks, for water
expands when it freezes. The loosened rock masses plough their way down
the steep, gathering, as they go, increasing power to tear away any
rocks in their path.

Wind blows finer rock fragments along, and they lodge in cracks. Fine
dust and the seeds of plants are lodged there. The rocky slopes of the
Yosemite Valley are all more or less covered with trees and shrubs that
have come from wind-sown seeds. These plants thrust their roots deeper
each year into the rock crevices. The feeding tips of roots secrete
acids that eat away lime and other substances that occur in rocks. Dead
leaves and other discarded portions of the trees rot about their roots,
and form soil of increasing depth. The largest trees grow on the rocky
soil deposited at the base of the slope. The tree's roots prevent the
river from carrying it off.

When granite crumbles, its different mineral elements are separated.
Clear, glassy particles of quartz we call sand. Dark particles of
feldspar become clay, and may harden into slate. Sand may become
sandstone. Exposed slate and sandstone are crumbled by exposure to wind
and frost and moving water, and are deposited again as sand-bars and
beds of clay.

The most interesting phase of soil study is the discovery of what a work
the humble earthworm does in mellowing and enriching the soil.

THE WORK OF EARTHWORMS

The farmer and the gardener should expect very poor crops if they
planted seed without first ploughing or spading the soil. Next, its fine
particles must be separated by the breaking of the hard clods. A wise
man ploughs heavy soil in the fall. It is caked into great clods which
crumble before planting time. The water in the clods freezes in winter.
The expansion due to freezing makes this soil water a force that
separates the fine particles. So the frost works for the farmer.

Just under the surface of the soil lives a host of workers which are our
patient friends. They work for their living, and are perhaps unconscious
of the fact that they are constantly increasing the fertility of the
soil. They are the earthworms, also called fishworms, which are
distributed all over the world. They are not generally known to farmers
and gardeners as friendly, useful creatures, and their services are
rarely noticed. We see robins pulling them out of the ground, and we are
likely to think the birds are ridding us of a garden pest. What we need
is to use our eyes, and to read the wonderful discoveries recorded in a
book called "Vegetable Mould and Earthworms," written by Charles
Darwin.

The benefits of ploughing and spading are the loosening and pulverizing
of the packed earth; the mixing of dead leaves and other vegetation on
and near the surface with the more solid earth farther down; the letting
in of water and air; and the checking of loss of water through cracks
the sun forms by baking the soil dry.

The earthworm is a creature of the dark. It cannot see, but it is
sufficiently sensitive to light to avoid the sun, the rays of which
would shrivel up its moist skin. Having no lungs or gills, the worm uses
the skin as the breathing organ; and it must be kept moist in order to
serve its important use. This is why earthworms are never seen above
ground except on rainy days, and never in the top soil if it has become
dry. In seasons of little rain, they go down where the earth is moist,
and venture to the surface only at night, when dew makes their coming up
possible.

Earthworms have no teeth, but they have a long snout that protrudes
beyond the mouth. Their food is found on and in the surface soil. They
will eat scraps of meat by sucking the juices, and scrape off the pulp
of leaves and root vegetables in much the same way. Much of their
subsistence is upon organic matter that can be extracted from the soil.
Quantities of earth are swallowed. It is rare that an earthworm is dug
up that does not show earth pellets somewhere on their way through the
long digestive canal. The rich juices of plant substance are absorbed
from these pellets as they pass through the body.

Earthworms explore the surface of the soil by night, and pick up what
they can find of fresh food. Nowhere have I heard of them as a nuisance
in gardens, but they eagerly feed on bits of meat, especially fat, and
on fresh leaves. They drag all such victuals into their burrows, and
begin the digestion of the food by pouring on it from their mouths a
secretion somewhat like pancreatic juice.

The worms honeycomb the earth with their burrows, which are long,
winding tubes. In dry or cold weather these burrows may reach eight feet
under ground. They run obliquely, as a rule, from the surface, and are
lined with a layer of the smooth soil, like soft paste, cast from the
body. The lining being spread, the burrow fits the worm's body closely.
This enables it to pass quickly from one end to the other, though it
must wriggle backward or forward without turning around.

At the lower end of the burrow, an enlarged chamber is found, where
hibernating worms coil and sleep together in winter. At the top, a
lining of dead leaves extends downward for a few inches, and in day time
a plug of the same material is the outside door. At night the worm comes
to the surface, and casts out the pellets of earth swallowed. The burrow
grows in length by the amount of earth scraped off by the long snout
and swallowed. The daily amount of excavation done is fairly estimated
by the castings observed each morning on the surface.

One earthworm's work for the farmer is not very much, but consider how
many are at work, and what each one is doing. It is boring holes through
the solid earth, and letting in the surface water and the air. It is
carrying the lower soil up to the surface, often the stubborn subsoil,
that no plough could reach. It is burying and thus hastening the decay
of plant fibre, which lightens heavy soil and makes it rich because it
is porous. Moreover, the earthworms are doing over and over again this
work of fining and turning over the soil, which the plough does but
seldom.

By the continuous carrying up of their castings, the earthworms
gradually bury manures spread on the surface. The collapse of their
burrows and the making of new ones keep the soil constantly in motion.
The particles are being loosened and brought into contact with the soil
water, that dissolves, and thus frees for the use of feeding roots, the
plant food stored in the rock particles that compose the mineral part of
the soil.

The weight of earth brought to the surface by worms in the course of a
year has been carefully estimated. Darwin gives seven to eighteen tons
per acre as the lowest and highest reports, based on careful collecting
of castings by four observers, working on small areas of totally
different soils. In England, earthworms have done a great deal more
toward burying boulders and ancient ruins than any other agency. They
eagerly burrow under heavy objects, the weight of which causes them to
crush the honeycombed earth. Undiscouraged, the earthworms repeat their
work.

"Long before man existed, the land was regularly ploughed, and continues
still to be ploughed by earthworms. It may be doubted whether there are
many other animals which have played so important a part in the history
of the world as have these lowly organized creatures."

After years of study, Charles Darwin came to this conclusion. The more
we study the lives of these earth-consuming creatures, the more fully do
we believe what the great nature student said. The fertile soil is made
of rock meal and decayed leaves and roots. Only recently have ploughs
been invented. But the great forest crops have grown in soil made mellow
by the earthworm's ploughing.

QUIET FORCES THAT DESTROY ROCKS

Wind and water are the blustering active agents we see at work tearing
down rocks and carrying away their particles. They do the most of this
work of levelling the land; but there are quiet forces at work which
might not attract our attention at all, and yet, without their help,
wind and running water would not accomplish half the work for which they
take the credit.

The air contains certain destructive gases which by their chemical
action separate the particles of the hardest rocks, causing them to
crumble. Now the wind blows away these crumbling particles, and the
solid unchanged rock beneath is again exposed to the crumbling agencies.

The changes in temperature between day and night cause rocks to contract
and expand, and these changes put a strain upon the mineral particles
that compose them. Much scaling of rock surfaces is due to these causes.
Building a fire on top of a rock, and then dashing water upon the heated
mass, shatters it in many directions. This process merely intensifies
the effect produced by the mild changes of winter and summer. Water is
present in most rocks, in surprising quantities, often filling the
spaces in porous rocks like sandstones.

When winter brings the temperature down to the freezing point, the water
near the surface of the rock first feels it. Ice forms, and every
particle of water is swollen by the change. A strain is put upon the
mineral particles against which the particles of ice crowd for more
room. Frost is a very powerful agent in the crumbling of rocks, as well
as of stubborn clods of earth. In warm climates, and in desert regions
where there is little moisture in the rocks, this destructive action of
freezing water is not known. In cold countries, and in high altitudes,
where the air is heavy with moisture, its greatest work is done.

Some kinds of rock decay when they become dry, and resist crumbling
better when they absorb a certain amount of moisture. Alternate wetting
and drying is destructive to certain rocks.

One of the unnoticed agents of rock decay is the action of lowly plants.
Mosses grow upon the faces of rocks, thrusting their tiny root processes
into pits they dig deeper by means of acids secreted by the delicate
tips. You have seen shaded green patches of lichens, like little rugs,
of different shapes, spread on the surface of rocks. But you cannot see
so well the work these growths are doing in etching away the surface,
and feeding upon the decaying mineral substance.

Mosses and lichens do a mighty work, with the help of water, in
reducing rocks to their original elements, and thus forming soil. No
plants but lichens and mosses can grow on the bare faces of rocks. As
their root-like processes lengthen and go deeper into the rock face,
particles are pried off, and the under-substance is attacked. Higher
plants then find a footing. Have you not seen little trees growing on a
patch of moss which gets its food from the air and the rock to which it
clings? The spongy moss cushion soaks up the rain and holds it against
the rock face. A streak of iron in the rock may cause the water to
follow and rust it out, leaving a distinct crevice. Now the roots of any
plant that happens to be growing on the moss may find a foot-hold in the
crack. Streaks of lime in a rock readily absorb water, which gradually
dissolves and absorbs its particles, inviting the roots to enter these
new passages and feed upon the disintegrating minerals. Dead leaves
decay, and the acids the trickling water absorbs from them are
especially active in disintegrating lime rocks.

From such small beginnings has resulted the shattering of great rock
masses by the growth of plants upon them. Tree roots that grow in rock
crevices exert a power that is irresistible. The roots of smaller plants
do the same great work in a quieter way.

When a hurricane or a flood tears down the mountain-side, sweeping
everything before it, trees, torn out by the roots, drag great masses
of rock and soil into the air, and fling them down the slope. Wind and
water thus finish the destruction which the humble mosses and lichens
began. What seemed an impregnable fortress of granite has crumbled into
fragments. Its particles are reduced to dust, or are on the way to this
condition. The plant food locked up in granite boulders becomes
available to hungry roots. Forests, grain-fields, and meadows cover the
work of destructive agencies with a mantle of green.

HOW ROCKS ARE MADE

The granite shaft is made out of the original substance of the earth's
crust. Its minerals are the elements out of which all of the rock masses
of the earth are formed, no matter how different they look from granite.
Sandstone is made of particles of quartz. Clay and slate are made out of
feldspar and mica. Iron ore comes from the hornblende in granite. The
mineral particles, reassembled in different proportions, form all of the
different rocks that are known.

Here in my hand is a piece of pudding-stone. It is made of pebbles of
different sizes, each made of different coloured minerals. The pebbles
are cemented together with a paste that has hardened into stone. This
kind of rock the geologists call _conglomerate_. Pudding-stone is the
common name, for the pebbles in the pasty matrix certainly do suggest
the currants and the raisins that are sprinkled through a Christmas
pudding.

Under the seashores there are forming to-day thick beds of sand. The
rivers bring the rock material down from the hills, and it is sorted and
laid down. The moving water drops the heaviest particles near shore, and
carries the finer ones farther out before letting them fall.

[Illustration: The town of Cripple Creek, Colorado, which has grown up
like magic since 1891, covers the richest gold and silver mines in the
world]

[Illustration: The level valley is filled up with fine rock flour washed
from the sides of the neighboring mountains]

The hard water, that comes through limestone rocks, adds lime in
solution to the ocean water. All the shellfish of the sea, and the
creatures with bony skeletons, take in the bone-building, shell-making
lime with their food. Generations of these inhabitants of the sea have
died, and their shells and bones have accumulated and been transformed
into thick beds of limestone on the ocean floor. This is going on
to-day; but the limestone does not accumulate as rapidly as when the
ocean teemed with shell-bearing creatures of gigantic size. Of these we
shall speak in another chapter.

The fine dust that is blown into the ocean from the land, and that makes
river water muddy, accumulates on the sea bottom as banks of mud, which
by the burden of later deposits is converted into clay. Sandstone is but
the compressed sand-bank.

In the study of mountains, geologists have discovered that old seashores
were thrown up into the first great ridges that form the backbone of a
mountain system. The Rocky Mountains, and the Appalachian system on the
east, were made out of thick strata of rocks that had been formed by
accumulations of mud and sand--the washings of the land--on the opposite
shores of a great mid-continental sea, that stretched from the crest of
one great mountain system across to the other, and north and south from
the Laurentian Hills to the Gulf of Mexico. The great weight of the
accumulating layers of rock materials on one side, and the wasted land
surfaces on the other, made the sea border a line of greatest weakness
in the crust of the earth. The shrinking of the globe underneath caused
the break; mashing and folding followed, throwing the ridge above
sea-level, and making dry land out of rock waste which had been
accumulating, perhaps for millions of years, under the sea. The
wrinkling of the earth's crust was the result of crushing forces which
produced tremendous heat.

Streams of lava sprang out through the fissures and poured streams of
melted rock down the sides of the fold, quite burying, in many places,
the layers of limestone, sandstone, and clay. Between the strata of
water-formed rocks there were often created chimney-like openings, into
which molten rock from below was forced, forming, when cool, veins and
dikes of rock material, specimens of the substance of the earth's
interior.

Tremendous pressure and heat, acting upon stratified rocks saturated
with water transform them into very different kinds of rock. Limestone,
subjected to these forces, is changed into marble. Clays are transformed
into slates. Sandstone is changed into quartzite, the sand grains being
melted so as to become no longer visible to the naked eye. The
anthracite coal of the Pennsylvania mountains is the result of heat and
pressure acting upon soft coal. Associated with these beds of hard coal
are beds of black lead, or graphite, the substance used in making "lead"
pencils. We believe that the same forces that operated to transform clay
rocks into slate, and limestone into marble, transformed soft coal into
hard, and hard coal into graphite, in the days when the earth was young.

The word _sedimentary_ is applied to rocks which were originally laid
down under water, as sediment, brought by running water, or by wind, or
by the decay of organic substances. _Stratified_ rocks are those which
are arranged in layers. Sedimentary rocks will fall into this class.
_Aqueous_ rocks are those which are formed under water. Most of the
stratified and sedimentary rocks, but not all, may be included under
this term. Rocks that are made out of fragments of other rocks torn down
by the agencies of erosion are called _fragmental_. Wind, water, and ice
are the three great agencies that wear away the land, bring rock
fragments long distances, and deposit them where aqueous rocks are being
formed. Volcanic eruptions bring material from the earth's interior.
This material ranges all the way from huge boulders to the finest
impalpable dust, called volcanic ashes. Rivers of ice called glaciers
crowd against their banks, loosening rock masses and carrying away
fragments of all sizes, in their progress down the valley. Brooks and
rivers carry the pebbles and the larger rock masses they are able to
loosen from their walls and beds, and grind them smooth as they move
along toward lower levels.

The air itself causes rocks to crumble; percolating water robs them of
their soluble salts, reducing even solid granite to a loose mass of
quartz grains and clay. Plants and animals absorb as food the mineral
substances of rocks, when they are dissolved in water. They transform
these food elements into their own body substance, and finally give back
their dead bodies, the mineral substances of which are freed by decay to
return to the earth, and become elements of rock again.

The decay of rock is well shown by the materials that accumulate at the
base of a cliff. Angular fragments of all sizes, but all more or less
flattened, come from strata of shaly rock, that can be seen jutting out
far above. A great deal of this sort of material is found mingled with
the soil of the Northeastern States. Round pebbles in pudding-stone have
been formed in brook beds and deposited on beaches where they have
become caked in mud and finally consolidated into rock. If the beach
chanced to be sandy instead of muddy, a matrix of sandy paste holds the
larger pebbles in place. Limestone paste cements together the pebbles of
limestone conglomerates.

In St. Augustine many of the houses are built of coquina rock, a mass of
broken shells which have become cemented together by lime mud, derived
from their own decay. On the slopes of volcanoes, rock fragments of all
kinds are cemented together by the flowing lava. So we see that there
are pudding-stones of many kinds to be found. If some solvent acid is
present in the water that percolates through these rocks it may soften
the cement and thus free the pebbles, reducing the conglomerate again to
a mere heap of shell fragments, or gravel, or rounded pebbles.

The story of rock formation tells how fire and water, and the two
combined, have made, and made over, again and again, the substance of
the earth's crust. Chemical and physical changes constantly tear down
some portions of the earth to build up others. The constant, combined
effort of wind and water is to level the earth and fill up the ocean
bed. Rocks are constantly being formed; the changes that have been going
on since the world began are still in progress. We can see them all
about us on any and every day of our lives.

GETTING ACQUAINTED WITH A RIVER

I have two friends whose childhood was spent in a home on the banks of a
noble eastern river. Their father taught the boy and the girl to row a
boat, and later each learned the more difficult art of managing a canoe.
On holidays they enjoyed no pleasure so much as a picnic on the
river-bank at some point that could be reached by rowing. As they grew
older, longer trips were planned, and the river was explored as far as
it was navigable by boat or canoe. Last summer when vacation came, these
two carried out a long-cherished plan to find the beginning of the
river--to follow it to its source. So they left home, and canoed
up-stream, until the stream became a brook, so shallow they could go no
farther. Then they followed it on foot--wading, climbing, making little
détours, but never losing the little river. At last they came to the
beginning of it--a tiny rivulet trickled out of the side of a hill,
filling a wooden keg that formed a basin, where thirsty passers-by could
stoop and drink. They decided to mark the spring, so that people who
found it later, and were refreshed by its clear water, might know that
here was born the greatest river of a great state. But they were not the
original discoverers. Above the spring, a board was nailed to a tree,
saying that this is the headwater of the river with the beautiful Indian
name, Susquehanna.

It was a dry summer, and the overflow of the basin was almost all drunk
up by the thirsty ground. They could scarcely follow it, except by the
groove cut by the rivulet in seasons when the flow was greater. They
followed the runaway brook, through the grass roots, that almost hid it.
As the ground grew steeper, it hurried faster. Soon it gathered the
water of other springs, which hurried toward it in small rivulets,
because its level was lower. Water always seeks the lowest level it can
find. Sometimes marshy spots were reached where water stood in the holes
made by the feet of cattle that came there to drink. The water was
muddy, and seemed to stand still. But it was settling steadily, and at
one side the little river was found, flowing away with the water it drew
from the swampy, springy ground. All the mud was gone, now; the water
was clear. It flowed in a bed with a stony floor, and there were rough
steps where the water fell down in little sheets, forming a waterfall,
the first of many that make this river beautiful in the upper half of
its course. To get from the high level of that hillside spring to the
low level of the sea, the water has to make a fall of twenty-three
hundred feet, but it makes the descent gradually. It could not climb
over anything, but always found a way to get around the rocks and hills
that stood in its way. When the flat marsh land interfered, the water
poured in and overflowed the basin at the lowest margin.

In the rocky ground the two explorers found that the stream had widened
its channel by entering a narrow crevice and wearing away its walls. The
continual washing of the water wears away stone. Rocks are softened by
being wet. Streaks of iron in the hardest granite will rust out and let
the water in. Then the lime in rocks is easily dissolved. Every dead
leaf the river carried along added an acid to the water, and this made
easier the process of dissolving the limestone.

Every crumbling rock gives the river tools that it uses like hammer and
chisel and sandpaper to smooth all the uneven surfaces in its bed, to
move stumbling blocks, and to dig the bed deeper and wider. The steeper
the slope is, the faster the stream flows, and the larger the rocks it
can carry. Rocks loosened from the stream bed are rolled along by the
current. Then bang! against the rocks that are not loose, and often they
are able to break them loose. The fine sand is swept along, and its
sharp points strike like steel needles, and do a great work in polishing
roughness and loosening small particles from the stream bed. The bigger
pebbles of the stream have banged against the rock walls, with the same
effect, smoothing away unevenness and pounding fragments loose, rolling
against one another, and getting their own rough corners worn away.

The makers of stone marbles learned their business from a brook. They
cut the stone into cubical blocks, and throw them into troughs, into
which is poured a stream of running water. The blocks are kept in
motion, and the grinding makes each block help the rest to grind off the
eight corners and the twelve ridges of each one. The water becomes muddy
with the fine particles, just as the drip from a grindstone becomes
unclean when an axe is ground. Pretty soon all the blocks in the trough
are changed into globes--the marbles that children buy at the shops when
marble season comes around.

I suppose if the troughs are not watched and emptied in time, the
marbles would gradually be ground down to the size of peas, then to the
size of small bird shot, and finally they would escape as muddy water
and fine sand grains.

Sure it is that the sandy shores that line most rivers are the remnants
of hard rocks that have been torn out and ground up by the action of the
current.

Not very many miles from its first waterfall the stream had grown so
large that my two friends knew that they would soon find their canoes.
The plan now was to float down the curious, winding river and to learn,
if the river and the banks could tell them, just why the course was so
crooked on the map. They came into a broad, level valley where streams
met them, coming out of deep clefts between the hills they were leaving
behind them. The banks were pebbly, but blackened with slimy mud that
made the water murky. The current swerved from one side to the other,
sometimes quite close to the bank, where the river turned and formed a
deep bend. On this side the bank was steep, the roots of plants and
trees exposed. On the opposite side a muddy bank sloped gently out into
the stream. Here building up was going on, to offset the tearing down.

The sharp bends are made sharper, once the current is deflected from the
middle of the stream to one side. At length the loops bend on each other
and come so near together that the current breaks through, leaving a
semicircular bayou of still water, and the river's course straightened
at that place. It must have been in a spring flood that this cut-off was
made, and, the break once made was easily widened, for the soil is fine
mud which, when soaked, crumbles and dissolves into muddy water.

Stately and slow that river moves down to the bay, into which it empties
its load. The rain that falls on hundreds of square miles of territory
flows into the streams that feed this trunk. The little spring that is
the headwater of the system is but one of many pockets in the hillsides
that hold the water that soaks into the ground and give it out by slow
degrees. Surface water after a rain flows quickly into the streams. It
is the springs that hold back their supply and keep the rivers from
running dry in hot weather.

Do they feel now that they know their river? Are they ready to leave it,
and explore some other? Indeed, no. They are barely introduced to it.
All kinds of rivers are shown by the different parts of this one. It is
a river of the mountains and of the lowland. It flows through woods and
prairies, through rocky passes and reedy flats. It races impetuously in
its youth, and plods sedately in later life. The trees and the other
plants that shadow this stream, and live by its bounty, are very
different in the upland and in the lowland. The scenery along this
stream shows endless variety. Up yonder all is wild. Down here great
bridges span the flood, boats of all kinds carry on the commerce between
two neighbour cities. A great park comes down to the river-bank on one
side. Canoes are thick as they can paddle on late summer afternoons.

No one can ever really know a river well enough to feel that it is an
old story. There is always something new it has to tell its friends. So
my two explorers say, and they know far more about their friendly river
than I do.

THE WAYS OF RIVERS

A canal is an artificial river, built to carry boats from one place to
another. Its course is, as nearly as possible, a straight line between
two points. A river, we all agree, is more beautiful than a canal, for
it winds in graceful curves, in and out among the hills, its waters
seeking the lowest level, always.

No artist could lay out curves more beautiful than the river forms.
These curves change from year to year, some slowly, some more rapidly.
It is not hard to understand just why these changes take place.

Some rivers are dangerous for boating at certain points. The current is
strong, and there are eddies and whirlpools that have to be avoided, or
the boat becomes unmanageable. People are drowned each season by
trusting themselves to rivers the dangerous tricks of which they do not
know. Deep holes are washed out of the bed of the stream by whirling
eddies. The pot-holes of which people talk are deep, rounded cavities,
ground out of the rocky stream-bed by the scouring of sand and loose
stones driven by whirling eddies in shallow basins. Every year deepens
each pot-hole until some change in the stream-bed shifts the eddy to
another place.

No stream finds its channel ready-made; it makes its own, and constantly
changes it. The current swings to one side of the channel, lifting the
loose sediment and grinding deeper the bed of the stream. The water lags
on the opposite side, and sediment falls to the bottom. So the
building-up of one side is going on at the same time that the
tearing-down process is being carried on on the other. With the lowering
of the bed the river swerves toward one bank, and a hollow is worn by
slow degrees. The current swings into this hollow, and in passing out is
thrown across the stream to the opposite bank. Here its force wears away
another hollow; and so it zigzags down-stream. The deeper the hollows,
the more curved becomes the course, if the general fall is but moderate.
It is toward the lower courses of the stream that the winding becomes
more noticeable. The sediment that is carried is deposited at the point
where the current is least strong, so that while the outcurves become
sharper by the tearing away of the stream's bank, the incurves become
sharper by the building up of this bank.

The Mississippi below Memphis is thrown into a wonderful series of
curves by the erosion and the deposit caused by the current zigzagging
back and forth from one bank to the other. Gradually the curves become
loops. The river's current finally jumps across the meeting of the
curves, and abandons the circular bend. It becomes a bayou or lagoon of
still water, while the current flows on in the straightened channel.
All rivers that flow through flat, swampy land show these intricate
winding channels and many lagoons that have once been curves of the
river.

No one would ever mistake a river for a lake or any other body of water,
yet rivers differ greatly in character. One tears its way along down its
steep, rock-encumbered channel between walls that rise as vertical
precipices on both sides. The roaming, angry waters are drawn into
whirlpools in one place. They lie stagnant as if sulking in another,
then leap boisterously over ledges of rock and are churned into creamy
foam at the bottom. Outside the mountainous part of its course this same
river flows broad and calm through a mud-banked channel, cut by
tributary streams that draw in the water of low, sloping hills.

The Missouri is such a wild mountain stream at its headwaters. We who
have seen its muddy waters from Sioux City to St. Louis would hardly
believe that its impetuous and picturesque youth could merge into an old
age so comfortable and placid and commonplace.

This thing is true of all rivers. They flow, gradually or suddenly, from
higher to lower levels. To reach the lowest level as soon as possible is
the end each river is striving toward. If it could, each river would cut
its bed to this depth at the first stage of its course. Its tools are
the rocks it carries, great and small. The force that uses these tools
is the power of falling water, represented by the current of the stream.
The upper part of a river such as the Missouri or Mississippi engages in
a campaign of widening and deepening its channel, and carrying away
quantities of sediment. The lower reaches of the stream flow through
more level country; the current is checked, and a vast burden of
sediment is laid down. Instead of tearing away its banks and bottom, the
river fills up gradually with mud. The current meanders between banks of
sediment over a bottom which becomes shallower year by year. The Rocky
Mountains are being carried to the Gulf of Mexico. The commerce of the
river is impeded by mountain débris deposited as mud-banks along the
river's lower course.

Many rivers are quiet and commonplace throughout their length. They flow
between low, rounded hills, and are joined by quiet streams, that occupy
the separating grooves between the hills. This is the oldest type of
river. It has done its work. Rainfall and stream-flow have brought the
level of the land nearly to the level of the stream. Very little more is
left to be ground down and carried away. The landscape is beautiful, but
it is no longer picturesque. Wind and water have smoothed away
unevennesses. Trees and grass and other vegetation check erosion, and
the river has little to do but to carry away the surface water that
falls as rain.

But suppose our river, flowing gently between its grassy banks, should
feel some mighty power lifting it up, with all its neighbour hills and
valleys, to form a wrinkle in the still unstable crust of the earth.
Away off at the river's mouth the level may not have changed, or that
region may have been depressed instead of elevated by the shrinking
process. Suppose the great upheaval has not severed the upper from the
lower courses of the stream. With tremendous force and speed, the
current flows from the higher levels to the lower. The river in the
highlands strikes hard to reach the level of its mouth. It grinds with
all its might, and all its rocky tools, upon its bed. All the mud is
scoured out, and then the underlying rocks are attacked. If these rocks
are soft and easily worn away, the channel deepens rapidly. One after
another the alternating layers are excavated, and the river flows in a
canyon which deepens more and more. As the level is lowered, the current
of the stream becomes slower and the cutting away of its bed less rapid.
The stream is content to flow gently, for it has almost reached the old
level, on which it flowed before the valley became a ridge or
table-land.

The rivers that flow in canyons have been thousands of years in carving
out their channels, yet they are newer, geologically speaking, than the
streams that drain the level prairie country. The earth has risen, and
the canyons have been carved since the prairies became rolling, level
ground.

[Illustration: This little pond is a basin hollowed by the same glacier
that scattered the stones and rounded the hills]

[Illustration: Every stream is wearing away its banks, while trees and
grass blades are holding on to the soil with all their roots]

The Colorado River flows through a canyon with walls that in places
present sheer vertical faces a mile in depth, and so smooth that no
trail can be found by which to reach from top to bottom. The region has
but slight erosion by wind, and practically none by rain. The local
rainfall is very slight. So the river is the one force that has acted to
cut down the rocks, and its force is all expended in the narrow area of
its own bed. Had frequent rains been the rule on the Colorado plateau,
the angles of the mesas would have been rounded into hills of the
familiar kind so constantly a part of the landscape in the eastern half
of the continent.

The Colorado is an ancient river which has to carry away the store of
moisture that comes from the Pacific Ocean and falls as snow on the high
peaks of the Rocky Mountains. Similar river gorges with similar stories
to tell are the Arkansas, the Platte, and the Yellowstone. All cut their
channels unaided through regions of little rain.

When the earth's crust is thrown up in mountain folds, and between them
valleys are formed, the level of rivers is sometimes lowered and the
rapidity of their flow is checked. A stream which has torn down its
walls at a rapid rate becomes a sluggish water-course, its current
clogged with sediment, which it has no power to carry farther. When such
a river begins to build and obstruct its own waters it bars its progress
and may form a lake as the outlet of its tributary streams. Many ancient
rivers have been utterly changed and some obliterated by general
movements of the earth's crust.

THE STORY OF A POND

Look out of the car window as you cross a flat stretch of new prairie
country, and you see a great many little ponds of water dotting the
green landscape. Forty years ago Iowa was a good place to see ponds of
all shapes and sizes. The copious rainfall of the early spring gathered
in the hollows of the land, and the stiff clay subsoil prevented the
water from soaking quickly into the ground. The ponds might dry away
during the hot, dry summer, leaving a baked clay basin, checked with an
intricate system of cracks. Or if rains were frequent and heavy, they
might keep full to the brim throughout the season.

Tall bulrushes stood around the margins of the largest ponds, and
water-lilies blossomed on the surface during the summer. The bass and
the treble of the spring chorus were made by frogs and toads and little
hylas, all of which resorted to the ponds to lay their eggs, in coiled
ropes or spongy masses, according to their various family traditions. On
many a spring night my zoölogy class and I have visited the squashy
margins of these ponds, and, by the light of a lantern, seen singing
toads and frogs sitting on bare hummocks of grass roots that stood
above the water-line. The throat of each musician was puffed out into a
bag about the size and shape of a small hen's egg; and all were singing
for dear life, and making a din that was almost ear-splitting at close
range. So great was the self-absorption of these singers that we could
approach them, daze them with the light of the lantern, and capture any
number of them with our long-handled nets before they noticed us. But it
was not easy to persuade them to sing in captivity, no matter how many
of the comforts of home we provided in the school aquariums. So, after
some very interesting nature studies, we always carried them back and
liberated them, where they could rejoin their kinsfolk and neighbours.

It was when we were scraping the mud from our rubber boots that we
realized the character of the bottoms of our prairie ponds. The slimy
black deposit was made partly of the clay bottom, but largely of
decaying roots and tops of water plants of various kinds. Whenever it
rained or the wind blew hard, the bottom was stirred enough to make the
water muddy; and on the quietest days a pail of pond water had a tinge
of brown because there were always decaying leaves and other rubbish to
stain its purity.

The farmers drained the ponds as fast as they were able, carrying the
water, by open ditches first, and later by underground tile drains, to
lower levels. Finally these trunk drain pipes discharged the water into
streams or lakes. To-day a large proportion of the pond areas of Iowa
has disappeared; the hollow tile of terra-cotta has been the most
efficient means of converting the waste land, covered by ponds, into
fertile fields.

But the ponds that have not been drained are smaller than they used to
be, and are on the straight road to extinction. This process one can see
at any time by visiting a pond. Every year a crop of reeds and a dozen
other species of vigorous water plants dies at the top and adds the
substance of their summer growth to the dust and other refuse that
gathers in the bottom of the pond. Each spring roots and seeds send up
another crop, if possible more vigorous than the last, and this top
growth in turn dies and lies upon the bottom. The pond level varies with
the rainfall of the years, but it averages a certain depth, from which
something is each year subtracted by the accumulations of rotting
vegetable matter in the bottom. Evaporation lowers the water-level,
especially in hot, dry summers. From year to year the water plants draw
in to form a smaller circle, the grassy meadow land encroaches on all
sides. The end of the story is the filling up of the pond basin with the
rotting substance of its own vegetation. This is what is happening to
ponds and inland marshes by slow degrees. The tile drain pipes
obliterate the pond in a single season. Nature is more deliberate. She
may require a hundred years to fill up a single pond which the farmer
can rid himself of by a few days of work and a few rods of tiling.

THE RIDDLE OF THE LOST ROCKS

Outside of my window two robins are building a nest in the crotch of a
blossoming red maple tree. And just across the hedge, men are digging a
big square hole in the ground--the cellar of our neighbour's new house.
It looks now as if the robins would get their house built first, for
they need but one room, and they do not trouble about a cellar. I shall
watch both houses as they grow through the breezy March days.

The brown sod was first torn up by a plough, which uncovered the red New
Jersey soil. Two men, with a team hitched to a scraper, have carried
load after load of the loose earth to a heap on the back of the lot,
while two other men with pickaxes dug into the hard subsoil, loosening
it, so that the scraper could scoop it up.

This subsoil is heavy, like clay, and it breaks apart into hard clods.
At the surface the men found a network of tree roots, about which the
soil easily crumbled. Often I hear a sharp, metallic stroke, unlike the
dull sound of the picks striking into the earth. The digger has struck a
stone, and he must work around it, pry it up and lift it out of the way.
A row of these stones is seen at one side of the cellar hole, ranged
along the bank. They are all different in size and shape, and red with
clay, so I can't tell what they are made of. But from this distance I
see plainly that they are irregular in form and have no sharp corners.
The soil strewn along the lot by the scraper is full of stones, mostly
irregular, but some rounded; some are as big as your head, others grade
down to the sizes of marbles.

When I went down and examined this red earth, I found pebbles of all
shapes and sizes, gravel in with the clay, and grains of sand. This
rock-sprinkled soil in New Jersey is very much like soil which I know
very well in Iowa; it looks different in colour, but those pebbles and
rock fragments must be explained in the same way here as there.

These are not native stones, the outcrop of near-by hillsides, but
strangers in this region. The stones in Iowa soil are also imported.

The prairie land of Iowa has not many big rocks on the surface, yet
enough of them to make trouble. The man who was ploughing kept a sharp
lookout, and swung his plough point away from a buried rock that showed
above ground, lest it should break the steel blade. One of the farmer's
jobs for the less busy season was to go out with sledge and dynamite
sticks, and blast into fragments the buried boulders too large to move.
Sometimes building a hot fire on the top of it, and throwing on water,
would crack the stubborn "dornick" into pieces small enough to be loaded
on stone-boats.

I remember when the last giant boulder whose buried bulk scarcely showed
at the surface, was fractured by dynamite. Its total weight proved to be
many tons. We hauled the pieces to the great stone pile which furnished
materials for walling the sides of a deep well and for laying the
foundation of the new house. Yet for years stones have been
accumulating, all of them turned out of the same farm, when pastures and
swampy land came under the plough.

Draw a line on the map from New York to St. Louis, and then turn
northward a little and extend it to the Yellowstone Park. The
boulder-strewn states lie north of this line, and are not found south of
it, anywhere. Canada has boulders just like those of our Northern
States. The same power scattered them over all of the vast northern half
of North America and a large part of Europe.

What explanation is there for this extensive distribution of unsorted
débris?

THE QUESTION ANSWERED

The rocks tell their own story, partly, but not wholly. They told just
enough to keep the early geologists guessing; and only very recently has
the guessing come upon the truth.

These things the rocks told:

1. We have come from a distance.

2. We have had our sharp corners worn off.

3. Many of us have deep scratches on our sides.

4. At various places we have been dumped in long ridges, mixed with much
earth.

5. A big boulder is often balanced on another one.

The first thing the geologist noted was the fact that these boulders are
strangers--that is, they are not the native rocks that outcrop on
hillsides and on mountain slopes near where they are found. Far to the
north are beds of rock from which this débris undoubtedly came. Could a
flood have scattered them as they are found? No, for water sorts the
rock débris it deposits, and it rounds and polishes rock fragments,
instead of scratching and grooving them and leaving them angular, as
these are.

Professor Agassiz went to Switzerland and studied the glaciers. He found
unsorted rock fragments where the glacier's nose melted, and let them
fall. They were worn and scratched and grooved, by being frozen into the
ice, and dragged over the rocky bed of the stream. The rocky walls of
the valley were scored by the glacier's tools. Rounded domes of rock
jutted out of the ground, in the paths of the ice streams, just like the
granite outcrop in Central Park in New York, and many others in the
region of scattered boulders.

After long studies in Europe and in North America, Professor Agassiz
declared his belief that a great ice-sheet once covered the northern
half of both countries, rounding the hills, scooping out the valleys and
lake basins, and scattering the boulders, gravel, and clay, as it
gradually melted away.

The belief of Professor Agassiz was not accepted at once, but further
studies prove that he guessed the riddle of the boulders. The rich soil
of the Northern States is the glacial drift--the mixture of rock
fragments of all sizes with fine boulder clay, left by the gradual
melting of the great ice-sheet as it retreated northward at the end of
the "Glacial Epoch."

GLACIERS AMONG THE ALPS

Switzerland is a little country without any seacoast, mountainous, with
steep, lofty peaks, and narrow valleys. The climate is cool and moist,
and snow falls the year round on the mountain slopes. A snow-cap covers
the lower peaks and ridges. Above the level of nine thousand feet the
bare peaks rise into a dry atmosphere; but below this altitude, and
above the six thousand-foot mark, lies the belt of greatest snowfall.
Peaks between six and nine thousand feet high are buried under the
Alpine snow-field, which adds thickness with each storm, and is drained
away to feed the rushing mountain streams in the lower valleys.

The snow that falls on the steep, smooth slope clings at first; but as
the thickness and the weight of these snow banks increase, their hold on
the slope weakens. They may slip off, at any moment. The village at the
foot of the slope is in danger of being buried under a snow-slide, which
people call an avalanche. "Challanche" is another name for it. The
hunter on the snow-clad mountains dares not shout for fear that his
voice, reëchoing among the silent mountains, may start an avalanche on
its deadly plunge into the valley.

On the surface of the snow-field, light snow-flakes rest. Under them the
snow is packed closer. Deeper down, the snow is granular, like pellets
of ice; and still under this is ice, made of snow under pressure. The
weight of the accumulated snow presses the underlying ice out into the
valleys. These streams are the glaciers--rivers of ice.

The glaciers of the Alps vary in length from five to fifteen miles, from
one to three miles in width, and from two hundred to six hundred feet in
thickness. They flow at the rate of from one to three feet a day, going
faster on the steeper slopes.

It is hard to believe that any substance as solid and brittle as ice can
flow. Its movement is like that of stiff molasses, or wax, or pitch. The
tremendous pressure of the snow-field pushes the mass of ice out into
the valleys, and its own weight, combined with the constant pressure
from behind, keeps it moving.

The glacier's progress is hindered by the uneven walls and bed of the
valley, and by any decrease in the slope of the bed. When a flat, broad
area is reached, a lake of ice may be formed. These are not frequent in
the Alps. The water near the banks and at the bottom of a river does not
flow as swiftly as in the middle and at the surface of the stream. The
flow of ice in a glacier is just so. Friction with the banks and bottom
retards the ice while the middle parts go forward, melting under the
strain, and freezing again. There is a constant readjusting of
particles, which does not affect the solidity of the mass.

The ice moulds itself over any unevenness in its bed if it cannot remove
the obstruction. The drop which would cause a small waterfall in a
river, makes a bend in the thick body of the ice river. Great cracks,
called _crevasses_, are made at the surface, along the line of the bend.
The width of the V-shaped openings depends upon the depth of the glacier
and the sharpness of the bend that causes the breaks.

Rocky ridges in the bed of the ice-stream may cause crevasses that run
lengthwise of the glacier. Snow may fill these chasms or bridge them
over. The hunter or the tourist who ventures on the glacier is in
constant danger, unless he sees solid ice under him. Men rope themselves
together in climbing over perilous places, so that if one slips into a
crevasse his mates can save him.

A glacier tears away and carries away quantities of rock and earth that
form the walls of its bed. As the valley narrows, tremendous pressure
crowds the ice against the sides, tearing trees out by the roots and
causing rock masses to fall on the top of the glacier, or to be dragged
along frozen solidly into its sides. The weight of the ice bears on the
bed of the glacier, and its progress crowds irresistibly against all
loose rock material. The glacier's tools are the rocks it carries frozen
into its icy walls and bottom. These rocks rub against the walls,
grinding off débris which is pushed or carried along. No matter how
heavy the boulders are that fall in the way of the ice river, the ice
carries them along. It cannot drop them as a river of water would do.
Slowly they travel, and finally stop where the nose of the glacier melts
and leaves all débris that the mountain stream, fed by the melting of
the ice, cannot carry away.

The bedrock under a glacier is scraped and ground and scored by the
glacier's tools--the rock fragments frozen into the bottom of the ice.
These rocks are worn away by constant grinding, just as a steel knife
becomes thin and narrow by use. Scratches and scorings and polished
surfaces are found in all rocks that pass one another in close contact.
Its worn-out tools the glacier drops at the point where its ice melts.
This great, unsorted mass of rock meal and coarser débris the stream is
gradually scattering down the valley.

The name "moraine" has been given to the earth rubbish a glacier
collects and finally dumps. The _top moraine_ is at the surface of the
ice. The _lateral moraines_, one at each side, are the débris gathered
from the sides of the valley. The _ground moraine_ is what débris the
ice pushes and drags along on the bottom. The _terminal moraine_ is the
dumping-ground of this mass of material, where the ice river melts.

Glaciers, like other rivers, often have tributary streams. A _median
moraine_, seen as a dark streak running lengthwise on the surface of a
glacier, means that two branch glaciers have united to form this one. Go
back far enough and you will reach the place where the two streams come
together. The two lateral moraines that join form the middle line of
débris, the median moraine. Three ice-streams joined produce two top
moraines. They locate the lateral moraines of the middle glacier.

The surface of a glacier is often a mass of broken and rough ice,
forming a series of pits and pinnacles that make crossing impossible.
The sun melts the surface, forming pools and percolating streams of
water, that honeycomb the mass. Underneath, the ice is tunnelled, and a
rushing stream flows out under the end of the glacier. It is not clear,
but black with mud, called _boulder clay_, or _till_, made of ground
rock, and mixed with fragments of all shapes and sizes. This is the meal
from the glacier's mill, dumped where the water can sift it.

"Balanced rocks" are boulders, one upon another, that once lay on a
glacier, and were left in this strange, unstable position when the
supporting ice walls melted away from them. In Bronx Park in New York
the "rocking stone" always attracts attention. The glacier that lodged
it there, also rounded the granite dome in Central Park and scattered
the rock-strewn boulder clay on Long Island. Doubtless in an earlier day
the edges of this glacier were thrust out into the Atlantic, not far
from the Great South Bay, and icebergs broke off and floated away.

[Illustration: Potsdam sandstone showing ripple marks]

[Illustration: _By permission of the American Museum of Natural History_

Glacial striæ on Lower Helderberg limestone]

[Illustration: Glacial grooves in the South Meadow, Central Park, New
York]

[Illustration: _By permission of the American Museum of Natural History_

Mt. Tom, West 83d St., New York]

Glaciers are small to-day compared with what they were long ago, in
Europe and in America. The climate became warmer, and the ice-cap
retreated. Old moraines show that the ice rivers of the Alps once came
much farther down the valleys than they do now. Smooth, deeply scored
domes of rock, the one in Central Park and the bald head of Mount Tom,
are just like those that lie in Alpine valleys from which the glaciers
have long ago retreated. There are old moraines far up the sides of
valleys, showing that once the glaciers were far deeper than now. No
other power could have brought rocks from strata higher up the
mountains, and lodged them thus.

Nearer home, Mt. Shasta and Mt. Rainier still have glaciers that have
dwindled in size, until they bear little comparison to the gigantic
ice-streams that once filled the smooth beds their puny successors flow
into. Remnants of glaciers lie in the hollows of the Sierras. We must go
north to find the snow-fields of Alaska and glaciers worthy to be
compared with those ancient ice rivers whose work is plainly to be seen,
though they are gone.

THE GREAT ICE-SHEET

Greenland is green only along its southern edge, and only in summer, so
its name is misleading. It is a frozen continent lying under a great
ice-cap, which covers 500,000 square miles and is several thousand feet
in thickness. The top of this icy table-land rises from five thousand to
ten thousand feet above the sea-level. The long, cold winters are marked
by great snowfall, and the drifts do not have time to melt during the
short summer; and so they keep getting deeper and deeper. Streams of ice
flow down the steeps into the sea, and break off by their weight when
they are pushed out into the water. These are the icebergs which float
off into the North Atlantic, and are often seen by passengers on
transatlantic steamers.

Long ago Greenland better deserved its name. Explorers who have climbed
the mountain steeps that guard the unknown ice-fields of the interior
have discovered, a thousand feet above the sea-level, an ancient beach,
strewn with shells of molluscs like those which now inhabit salt water,
and skeletons of fishes lie buried in the sand. It is impossible to
think that the ocean has subsided. The only explanation that accounts
for the ancient beach, high and dry on the side of Greenland's icy
mountain is that the continent has been lifted a thousand feet above its
former level. This is an accepted fact.

We know that climate changes with changed altitude as well as latitude.
Going up the side of a mountain, even in tropical regions, we may reach
the snow-line in the middle of summer. Magnolia trees and tree ferns
once grew luxuriantly in Greenland forests. Their fossil remains have
been found in the rocks. This was long before the continent was lifted
into the altitude of ice and snow. And it is believed that the climate
of northern latitudes has become more severe than formerly from other
causes. It is possible that the earth's orbit has gradually changed in
form and position.

If Greenland should ever subside until the ancient beach rests again at
sea-level, the secrets of that unknown land would be revealed by the
melting of the glacial sheet that overspreads it. Possibly it would turn
out to be a mere flock of islands. We can only guess. North America had,
not so long ago, two-thirds of its area covered with an ice-sheet like
that of Greenland, and a climate as cold as Greenland's. At this time
the land was lifted two to three thousand feet higher than its present
level. All of the rain fell as snow, and the ice accumulated and became
thicker year by year. Instead of glaciers filling the gorges, a great
ice flood covered all the land, and pushed southward as far as the Ohio
River on the east and Yellowstone Park in the west. The Rocky Mountains
and some parts of the Appalachian system accumulated snow and formed
local glaciers, separated from the vast ice-sheet.

The unstable crust of the earth began to sink at length, and gradually
the ice-sheet's progress southward was checked, and it began to recede
by melting. All along the borders of this great fan-shaped ice-field
water accumulated from the melting, and flooded the streams which
drained it to the Atlantic and the Gulf. Icebergs broken off of the edge
of the retiring ice-sheet floated in a great inland sea. The land sank
lower and lower until the general level was five hundred to one thousand
feet lower than it now is. The climate became correspondingly warm, and
the icebergs melted away. Then the land rose again, and in time the
inland sea was drained away into the ocean, except for the waters that
remained in thousands of lakes great and small that now occupy the
region covered by the ice.

Ancient sea beaches mark the level of high water at the time that the
flood followed the melting ice. On the shores of Lake Champlain, but
nearly five hundred feet higher than the present level of the lake,
curious geologists have found many kinds of marine shells on a
well-marked old sea beach. The members of one exploring party in the
same region were surprised and delighted to come by digging upon the
skeleton of a whale that had drifted ashore in the ancient days when
the inland sea joined the Atlantic.

Lake Ontario's ancient beach is five hundred feet above the present
water-level; Lake Erie's is two hundred fifty feet above it; Lake
Superior's three hundred thirty feet higher than the present beach. No
doubt when the water stood at the highest level, the Great Lakes formed
one single sheet of water which settled to a lower level as the rivers
flowing south cut their channels deep enough to draw off the water
toward the Gulf. Lake Winnipeg is now the small remnant of a vast lake
the shores of which have been traced. The Minnesota River finally made
its way into the Mississippi and drained this great area the stranded
beaches of which still remain. The name of Agassiz has been given to the
ancient lake formed by the glacial flood and drained away thousands of
years ago but not until it had built the terraced beach which locates it
on the geological map of the region.

When the ice-sheet came down from the north it dragged along all of the
soil and loose rock material that lay in its path. With the boulders
frozen into its lower surface it scratched and grooved the firm bedrock
over which it slid, and rounded it to a smooth and billowy surface. The
progress of the ice-sheet was southward, but it spread like a fan so
that its widening border turned to east and west.

When it reached its southernmost limit and began to melt, it laid down a
great ridge of unsorted rock material, remnants of which remain to this
day,--the terminal moraine of the ancient ice-sheet. The line of this
ancient deposit starts on Long Island, crosses New Jersey and
Pennsylvania, then dips southward, following the general course of the
Ohio River to its mouth, forming bluffs in southern Ohio, Indiana, and
Illinois. The line bends upward as it crosses central Missouri, a corner
of Kansas, and eastern Nebraska, parallel with the course of the
Missouri.

As the ice-sheet melted, boulders were dropped all over the Northern
States and Canada. These were both angular and rounded. In some places
they are scattered thickly over the surface and are so numerous as to be
a great hindrance to agriculture. In many places great boulders of
thousands of tons weight are perched on very slight foundations, just
where they lodged when the ice went off and left them, after carrying
them hundreds of miles. Around them are scattered quantities of loose
rock material, not scored or ground as are those which were carried on
the under-surface of the glacial ice. These unscarred fragments rode on
the top of the ice. They were a part of the top moraine of the glacial
sheet.

The finest material deposited is rock meal, ground by the great glacial
mill, and called "boulder clay." It is a stiff, dense, stony paste in
which boulders of all sizes, gravel, pebbles, and cobblestones are
cemented.

The "drift" of the ice-sheet is the rubbish, coarse and fine, it left
behind as it retreated. Below the Ohio River there is a deep soil
produced by the decay of rocks that lie under it. North of Ohio is
spread that peculiar mixture of earth and rock fragments which was
transported from the north and spread over the land which the ice-sheet
swept bare and ground smooth and polished.

The drift has been washed away in places by the floods that followed the
ice. Granite domes are thus exposed, the grooves and scratches of which
tell in what direction the ice flood was travelling. Miles away from
that scored granite, but in the same direction as the scratches,
scattered fragments of the same foundation rock cover fields and
meadows. Thus, much of the drift material can be traced to its original
home, and the course of the ice-sheet can be determined. Many immense
boulders the home of which was in the northern highlands of Canada rode
southward, frozen into icebergs that floated in the great inland sea.
Great quantities of débris were added to the original glacial drift
through the agency of these floating ice masses, which melted by slow
degrees.

FOLLOWING SOME LOST RIVERS

What would you think if the boat in which you were floating down a
pleasant river should suddenly grate upon sand, and you should look over
the gunwale and find that here the waters sank out of sight, the river
ended? I believe you would rub your eyes, and feel sure that you were
dreaming. Do not all rivers flow along their beds, growing larger with
every mile, and finally empty their waters into a sea, or bay, or lake,
or flow into some larger stream? This is the way of most rivers, but
there are exceptions. In the Far West there are some great rivers that
absolutely disappear before they reach a larger body of water. They
simply sink away into the sand, and sometimes reappear to finish their
courses after flowing underground for miles. Do you know the name of one
great western river of which I am thinking? Is there any stream in your
neighbourhood which has such peculiar ways?

Down in Kentucky there is a region where, it is said, one may walk fifty
miles without crossing running water. In the middle of our country, in
the region of plentiful rainfall, and in a state covered with beautiful
woodlands and famous for blue grass and other grain crops, it is
amazing that, over a large area, brooks and larger streams are lacking.
In most of the state there is plenty of water flowing in streams like
those in other parts of the eastern half of the United States. In the
near neighbourhood of this peculiar section of the state the streams
come to an end suddenly, pouring their water into funnel-shaped
depressions of the ground called sink-holes. After a heavy rain the
surface water, accumulating in rivulets, may also be traced to small
depressions which seem like leaks in the earth's crust, into which the
water trickles and disappears.

It must have been noticed by the early settlers who came over the
mountains from the eastern colonies, and settled in the new, wild, hilly
country, which they called Kentucky. The first settlers built their log
cabins along the streams they found, and shot deer and wild turkey and
other game that was plentiful in the woods. The deer showed them where
salt was to be found in earthy deposits near the streams; for salt is
necessary to every creature. Deer trails led from many directions to the
"salt licks" which the wild animals visited frequently.

Perhaps the same pioneers who dug the salt out of the earth found
likewise deposits of _nitre_, called also _saltpetre_, a very precious
mineral, for it is one of the elements necessary in the manufacture of
gunpowder. With the Indians all about him, and often showing themselves
unfriendly, the pioneer counted gunpowder a necessity of life. He relied
on his gun to defend and to feed his family. There were men among those
first settlers who knew how to make gunpowder, and saltpetre was one of
the things that had to be carried across the mountains into Kentucky,
until they found it in the hills. No wonder that prospectors went about
looking for nitre beds in the overhanging ledges of rocks along
stream-beds. In such situations the deposits of nitre were found. The
earth was washed in troughs of running water to remove the clayey
impurity. After a filtering through wood-ashes, the water which held the
nitre in solution was boiled down, and left to evaporate, after which
the crystals of saltpetre remained.

Solid masses of saltpetre weighing hundreds of pounds were sometimes
found in protected corners under shelving rocks. It was no doubt in the
fascinating hunt for lumps of this pure nitre that the early prospectors
discovered that the streams which disappeared into the sink-holes made
their way into caverns underground. Digging in the sides of ravines
often made the earthy wall cave in, and the surprised prospector stood
at the door of a cavern. The discoverer of a cave had hopes that by
entering he might find nitre beds richer than those he could uncover on
the surface, and this often turned out to be true. The hope of finding
precious metals and beds of iron ore also encouraged the exploration of
these caves. By the time the war of 1812 was declared, the mining of
saltpetre was a good-sized industry in Kentucky. Most of the mineral was
taken out of small caves, and shipped, when purified, over the
mountains, on mule-back by trails, and in carts over good roads that
were built on purpose to bring this mineral product to market. As long
as war threatened the country, the Government was ready to buy all the
saltpetre the Kentucky frontiersmen could produce. And the miners were
constantly in search of richer beds that promised better returns for
their labour.

It was this search that led to the exploration of the caves discovered,
although the explorer took his life in his hands when he left the
daylight behind him and plunged into the under-world.

Not all lost rivers tell as interesting stories or reveal as valuable
secrets as did those the neighbours of Daniel Boone traced along their
dark passages underground, and finally saw emerge as hillside springs,
in many cases, to feed Kentucky rivers. But it is plain that no river
sinks from sight unless it finds porous or honeycombed rocks that let it
through. The water seeks the nearest and easiest route to the sea. Its
weight presses toward the lowest level, always. The more water absorbs
of acid, the more powerfully does it attack and carry away the substance
of lime rocks through which it passes.

THE MAMMOTH CAVE OF KENTUCKY

There is no more fertile soil in the country than that of the famous
blue grass region of Kentucky. The surface soil rests upon a deep
foundation of limestone rocks, and very gradually the plant food locked
up in these underlying strata is pulled up to the surface by the soil
water, and greedily appropriated by the roots of the plants.

Part of the water of the abundant rainfall of this region soaks into the
layers of the lime rock, carrying various acids in solution which give
it power to dissolve the limestone particles, and thus to make its way
easily through comparatively porous rock to the very depths of the
earth. So it has come about that the surface of the earth is undermined.
Vast empty chambers have been carved by the patient work of trickling
water, which has carried away the lime that once formed solid and
continuous layers of the earth's crust. We must believe that the work
has taken thousands of years, at least, for no perceptible change has
come to these wonderful caves since the discovery and exploration of
them a century and more ago.

The streams that flow into the region of these caves disappear suddenly
into sink-holes and flow through caverns. After wearing away their
subterranean channels, leaping down from one level to another, forming
waterfalls and lakes, some emerge finally through hillsides in the form
of springs.

The cavern region of Kentucky covers eight thousand square miles. The
underground chambers found there are in the limestone rock which varies
from ten to four hundred feet in thickness, and averages a little less
than two hundred feet. Over this territory the number of sink-holes
average one hundred to the square mile; and the streams that have poured
their water into these basins have made a network of open caverns one
hundred thousand miles in length.

A great many small caverns have been thoroughly explored and are famous
for their beauty. The Diamond Cave is one of the most splendid, for it
is lined with walls and pillars of alabaster that sparkle in the
torchlight with crystals that look like veritable diamonds. Beautiful
springs and waterfalls are found in many caves, but the grandest of all
is the Mammoth Cave, beside which no other is counted worthy to be
compared.

Great tales the miners told of the wonder and the beauty of these
caverns, the walls of which were supported by arching alabaster columns
and wonderful domes, of indescribable beauty of form and colouring. In
1799, the year that Washington died, a pioneer discovered the entrance
to a cave, the size and beauty of which surpassed anything he had seen
before. After exploring it for a short distance he returned home and
took his whole family with him to enjoy the first view of the wonderful
cavern he had discovered. They carried pine knots and a lighted torch,
by which they made their way for some distance, but the torch was
accidentally extinguished and they groped their way in darkness and
missed the entrance. Without anything to guide them, they wandered in
darkness for three days, and were almost dead when at last they stumbled
upon the exit. This is the doorway of the Mammoth Cave of Kentucky, one
of the wonders of the world.

This was a terrible experience. The next persons who attempted to
explore the new cave were better provisioned against the chance of
spending some time underground. The pioneers found rich deposits of
nitre in the "Great Cave," as they called it. Scientists visited it and
explored many of its chambers. The reputation of this cavern has been
spread by thousands of visitors who have come from all over the world to
see it. The cave has not yet been completely explored. The regular
tours, on which the guides conduct visitors, cover but a small part of
the one hundred and fifty miles measured by the two hundred or more
avenues. The passages wind in and out, crossing each other, sometimes at
different levels, and forming a network of avenues in which the
unaccustomed traveller would surely be lost. The old guides know every
inch of their regular course, and their quaint and edifying talk adds
greatly to the pleasure of the visitors.

From the hotel, parties are organized for ten o'clock in the morning and
seven o'clock in the evening. Each visitor is provided with a lard-oil
lamp. The guide carries a flask of oil and plenty of matches. No special
garb is necessary, though people usually dress for comfort, and wear
easy shoes. The temperature of the cave is uniform winter and summer,
varying between fifty-three and fifty-four degrees Fahrenheit.

The cave entrance is an arch of seventy-foot span in the hillside. A
winding flight of seventy stone steps leads the party around a
waterfall, into a great chamber under the rocks. Then the way goes
through a narrow passage, where the guide unlocks an iron gate to let
them in. The visitors now leave all thoughts of daylight behind, for the
breeze that put out their lights as they entered the cave is past, and
they stand in the Rotunda, a vast high-ceilinged chamber, silent and
impressive, with walls of creamy limestone, encrusted with gypsum, which
has been stained black by manganese. From the vestibule on, each passage
and each room has a name, based upon some historic event or some fancied
resemblance. The Giant's Coffin is a great kite-shaped rock lying in one
of the rooms of the cave. The Star Chamber has a wonderful
crystal-studded dome in which the guide produces the effect of a sunrise
by burning coloured lights. Bonfires built at suitable points produce
wonderful shadow effects, which are like nothing else in the world. The
old saltpetre vats which the visitors pass in taking the "Long Route"
through the cave, point them back to the days during the War of 1812,
when this valuable mineral was extracted from the earth in the floor of
the cave. The industry greatly enriched the thrifty owners of the cave,
but the works were abandoned after peace was declared.

It must be a wonderful experience to walk steadily for nine hours over
the Long Route, for so pure is the air and so wonderful is the scenery
that people rarely complain of fatigue when the experience is over.
There is no dust on the floors of these subterranean chambers, and they
are not damp except near places where water trickles, here and there, in
rivulets and cascades. Pools of water at the bottoms of pits so deep
that a lighted torch requires several seconds to reach the bottom, and
rivers and lakes of considerable size, show where some of the surface
water goes to. A strange underground suction creates whirlpools in some
of these streams. People go in boats holding twenty passengers for a row
on Echo River, and the guide dips up with a net the blind fish and
crayfish and cave lizards which inhabit these subterranean waters. The
echoes in various chambers of the Mammoth Cave are remarkable. In some
of them a song by a single voice comes back with full chords, as if
several voices carried the different parts. The single notes of flute
and cornet are returned with the same beautiful harmonies. A pistol shot
is given back a dozen times, the sound rebounding like a ball from rock
to rock of the arching walls. The vibrations of the water made by the
rower's paddles reëcho in sounds like bell notes, and they are
multiplied into harmonies that suggest the chimes in the belfry of a
cathedral.

The walls of various chambers differ from each other according to the
minerals that compose them. Some are creamy white limestone arches, some
are walled with black gypsum, some are hung with great curtains of
stalagmites, solid but suggesting the lightness and grace of folds of
crêpe. Under such hangings the floor is built up in stalactites. The
mineral-laden water, the constant drip of which has produced a hanging,
icicle-like stalagmite, has built up the stalactite to meet it.

Probably nothing is more beautiful than the flower-like crystals that
bloom all over the walls of a chamber called "Mary's Bower." The floor,
even, sparkles with jewels that have fallen from the wonderful and
delicate flower clusters built from deposits of the lime-laden water
which goes on building and replacing the bits that fall. "Martha's
Vineyard" is decorated with nodules, like bunches of grapes, that
glisten as if the dew were on them. The white gypsum in some caves makes
the walls look as if they were carved out of snow. Still others have
clear, transparent crystals that make them gleam in the torches' light
as if the walls were encrusted with diamonds.

The cave region of Indiana is also famous. The great Wyandotte Cave in
Crawford County is the most noted of many similar caverns. In some of
the chambers, bats are found clinging to the ceiling, heads downward,
like swarms of bees. The caverns of Luray, in Virginia, are complex and
wonderful in their structure, and famous for the beautiful stalactites
and stalagmites they contain. But there is no cave in this country so
wonderful and so grand in its dimensions as the Mammoth Cave in
Kentucky.

LAND-BUILDING BY RIVERS

Once a year, when the rainy season comes in the mountainous country
south of Egypt, the old Nile floods its banks and spreads its slimy
waters over the land, covering the low plains to the very edge of the
Sahara Desert. The people know it is coming, and are prepared for this
flood. We should think such an overflow of our nearest river a monstrous
calamity, but the Egyptians bless the river which blesses them. They
know that without the Nile's overflow their country would be added to
the Desert of Sahara. In a short time after the overflow, the river
reaches its highest point and begins to ebb. Canals lying parallel to
its course are filled with water which is saved for use in the hot, dry
summer. As the flood goes down, a deposit of slimy mud lies as a rich
fertilizer on the land. It is this and the water which the earth has
absorbed that make Egypt one of the most fertile agricultural countries
in the world.

The region covered by the Nile's overflow is the flood plain of this
river. On this plain the Pyramids, the Sphinx, and other famous
monuments of Egypt stand. The statue of Rameses II. built 3,000 years
ago, has its base buried nine feet deep in the rich soil made of Nile
sediment. A well dug in this region goes through forty feet of this soil
before striking the underlying sand. How many years ago did the first
Nile overflow take place? We may begin our calculation by finding out
the average yearly deposit. It is a slow process that accumulates but
nine feet in 3,000 years. If you were in Egypt when the Nile went back
into its banks, you would see that the scum it leaves in a single
overflow adds not a great deal to the thickness of the soil. Possibly
floods have varied in their deposits from year to year, so that any
calculation of the time it took to build that forty feet of surface soil
must be but a rough estimate. This much we know: it has been an
uninterrupted process which has taken place within the present
geological epoch, "the Age of Man."

Not all the rich sediment the Nile brings down is left on the level
flood plain along its course. A vast quantity is dumped at the river's
mouth, where the tides of the Mediterranean check the river's current.
Thus the great delta is formed. The broad river splits into many mouths
that spread out like a fan and build higher and broader each year the
mud-banks between the streams. Upper Egypt consists of river swamps.
Lower Egypt, from Cairo to the sea, is the delta built by the river
itself on sea bottom. From the head of the delta, where the river
commences to divide, to the sea, is an area of 10,000 square miles made
out of material contributed by upper Egypt, and built by the river.
Layer upon layer, it is constantly forming, but most rapidly during the
season of floods.

Coming closer home, let us look at the map of the Mississippi Valley.
Begin as far north as St. Louis. For the rest of its course the
Mississippi River flows through a widening plain of swamp land, flooded
in rainy seasons. Through this swampy flood plain the river meanders;
its current, heavily loaded with sediment, swings from one side to the
other of the channel, building up here, wearing away there, and
straightening its course when the curves become so sharp that their
sides meet. Then the current breaks through the thin wall, and a bayou
of still water is left behind.

Below Baton Rouge the Mississippi breaks into many mouths, that spread
and carry the water of the great river into the Gulf of Mexico. The Nile
delta is triangular, like delta, [Greek: D], the fourth letter of the
Greek alphabet; but the Mississippi's delta is very irregular. The main
mouth of the river flows fifty miles out into the Gulf between
mud-banks, narrow and low. At the tip it branches into several streams.

From the mouth of the Ohio to the Gulf, the Mississippi flood plain
covers 30,000 square miles. Over this area, sediment to an average depth
of fifty feet has been laid down. In earlier times the river flooded
this whole area, when freshets swelled its tributaries in the spring.
The flood plain then became a sea, in the middle of which the river's
current flowed swiftly. The slow-flowing water on each side of the main
current let go of its burden of sediment and formed a double ridge.
Between these two natural walls the main river flowed. When its level
fell, two side streams, running parallel with the main river drained the
flood plains on each side into the main tributaries to right and left.
These natural walls deposited when the river was in flood are called
_levees_. Each heavy flood builds them higher, and the bed of the stream
rises by deposits of sediment. So it happens that the level of the river
bed is higher than the level of its flood plain.

This is an interesting fact in geology. But the people who have taken
possession of the rich flood plain of the Mississippi River, who have
built their homes there, drained and cultivated the land, and built
cities and towns on the areas reclaimed from swamps, recognize the
elevation of the river bed as the greatest danger that threatens them.
Suppose a flood should come. Even if it does not overflow the levees, it
may break through the natural banks and thus overflow the cities and the
farm lands to left and right.

Instead of living in constant fear of such a calamity, the people of the
Mississippi flood plain have sought safety by making artificial levees,
to make floods impossible. These are built upon the natural levees. As
the river bed rises by the deposit of mud, the levees are built higher
to contain the rising waters. No longer does the rich soil of the
Mississippi flood plain receive layers of sediment from the river's
overflow. The river very rarely breaks through a levee. The United
States Government has spent great sums in walling in the river, and each
state along its banks does its share toward paying for this
self-protection.

By means of _jetties_ the river's current is directed into a
straightened course, and its power is expended upon the work of
deepening its own channel and carrying its sediment to the Gulf. Much as
the river has been forced to do in cleaning its own main channel,
dredging is needed at various harbours to keep the river deep enough for
navigation. The forests of the mountain slopes in Colorado are being
slaughtered, and the headwaters of the Missouri are carrying more and
more rocky débris to choke the current of the Mississippi. Colorado soil
is stolen to build land in the vast delta, which is pushing out into the
Gulf at the rate of six miles in a century--a mile in every sixteen
years. The Mississippi delta measures 14,000 square miles. With the
continued denuding of mountain slopes, we shall expect the rate of delta
growth to be greatly increased, until reforesting checks the destructive
work of wind and water.

THE MAKING OF MOUNTAINS

The gradual thickening and shrinking of the earth's crust as it cools
have made the wrinkles we call mountain systems. Through millions of
years the globe has been giving off heat to the cold sky spaces through
which it swings in its orbit around the sun. The cooling caused the
contraction of the outer layer to fit the shrinking of the mass. When a
plump peach dries on its pit, the skin wrinkles down to fit the dried
flesh. The fruit shrinks by loss of water, just as the face of an old
person shrinks by loss of fat. The skin becomes wrinkled in both cases.

The weakest places in the earth's crust were the places to crumple,
because they could not resist the lateral pressure that was exerted by
the shrinking process. Along the shores of the ancient seas the rivers
piled great burdens of sediment. This caused the thin crust to sink and
to become a basin alongside of a ridge. The wearing away of the land in
certain places lightened and weakened the crust at these places, so that
it bent upward in a ridge.

Perhaps the first wrinkles were not very high and deep. The gradual
cooling must have exerted continued pressure, and the wrinkles have
become larger. It is not likely that new wrinkles would be formed as
long as the old ones would crumple and draw up into narrower, steeper
slopes, in response to the lateral crushing.

We can imagine those first mountains rising as folds under the sea.
Gradually their bases were narrowed, and their crests lifted out of the
water. They rose as long, narrow islands, and grew in size as time went
on.

Why is the trend of the great mountain systems almost always north and
south? Study the map of the continents and see how few cross ranges are
shown, and how short they are, compared with the others. The molten
globe bulged at its equator, as it rotated on its axis. The moon added
its strong pulling force to make it bulge still more. As the crust
thickened, it became less responsive to the two forces that caused it to
bulge. The shrinkage was greatest where the globe had been most pulled
out of shape. The rate of the earth's rotation is believed to have
diminished. Every change tended to let the earth draw in its (imaginary)
belt, a notch at a time. The forces of contraction acted along the line
of the equator, and formed folds running toward the poles. In this early
time the great mountain systems were born, and they grew in size
gradually, from small beginnings.

These mountains of upheaval, made by the bending of the earth's crust,
and the formation of alternating ridges and depressed valleys, are many.
The earth is old and much wrinkled. Other mountains have been formed by
forces quite different. Volcanic mountains have been far more numerous
in ages gone than they are now.

Mt. Hood and Mt. Rainier are peaks built up by the materials thrown out
of the craters of volcanoes dead these thousands of years. Vesuvius is
at present showing us how volcanic mountains are made. Each eruption
builds larger the cone--that is, the chimney through which the molten
rocks, the ashes, and the steam are ejected. Side craters may open, the
main cone be broken and its form changed, but the mass of lava and
stones and ashes grows with each eruption. The mountain grows by the
additions it receives. Ætna is a mountain built of lava.

A third mountain system grew, not by addition, but by subtraction. The
Catskills illustrate this type. This group of mountains is the remnant
of a table-land made of level layers of red sandstone. The rest of the
high plain has been cut down and carried away, leaving these picturesque
hills, the survival of which is as much a mystery as the disappearance
of the balance of the plateau of which they were once a part.

The fold that forms a typical mountain ridge has a cone of granite, the
original rock foundation of the earth, and on this are layers of
stratified rock, ancient deposits of sediment carried to the sea by
streams. When exposed to wind and rain, the ridge is gradually worn
down. In some places the water cuts away the soft rock and forms a
stream-bed, that cuts deeper and deeper, using the rock fragments as its
tools. Often the layers of aqueous rocks are cut through, and the
granite exposed.

Sometimes the hardest stratified rock-beds resist the water and the wind
and are left as a series of ridges along the sides of the main range.
The crumpling forces may crack the ridge open for its whole length, and
one side of the chasm may slip down and the other go up. The result is a
sheer wall of exposed rock strata, layers of which correspond with those
that lie far below the top of the portion that slid down in the great
upheaval and subsidence that parted them. These slips are known as
_faults_.

THE LAVA FLOOD OF THE NORTHWEST

We know little about the substance that occupies the four thousand miles
of distance between the surface and the centre of our earth. We know
that the terrible weight borne by the central mass compresses it, so
that the interior must grow denser as the core is approached. Scientists
have weighed the earth, and tell us that the crust is lighter than the
rest. The supposition is that there is a great deal of iron in the
interior, and possibly precious metals, too.

Our deepest wells and mines go down about a mile, then digging stops, on
account of the excessive heat. But the crumpling of the crust, and the
wearing away of the folded strata by wind and running water, have laid
bare rocks several miles in thickness on the slopes of mountains, and
exposed the underlying granite, on which the first sedimentary rocks
were deposited. On this granite lie stratified rocks, which are
crystalline in texture. These are the beds, sometimes miles in depth,
called _metamorphic_ rocks, formed by water, then transformed by heat.

The wearing away of rocks by wind and water has furnished the materials
out of which the aqueous rocks have been made. Layers upon layers of
sandstone, shales, limestone, and the like, are exposed when a river
cuts a canyon through a plateau. The layered deposits of débris at the
mouth of the river make new aqueous rocks out of old. Every sandy beach
is sandstone in the making. This work is never ended.

In the early days the earth's crust often gaped open in a mighty crater
and let a flood of lava overspread the surface. The ocean floor often
received this flood of melted rock. In many places the same chimney
opened again and again, each time spreading a new layer of lava on top
of the old, so that the surface has several lava sheets overlying the
aqueous strata.

If the hardened lava sheet proved a barrier to the rising tide of molten
lava in the chimney it was often forced out in sheets between the layers
of aqueous rocks. Wherever the heated material came into contact with
aqueous rocks it transformed them, for a foot or more, into crystalline,
metamorphic rocks.

A chimney of lava is called a _dike_. In mountainous countries dikes are
common. Sometimes small, they may also be hundreds of feet across, often
standing high above the softer strata, which rains have worn away. Dikes
often look like ruined walls, and may be traced for miles where they
have been overturned in the mountain-making process.

The great lava flood of the Northwest happened when the Coast Range was
born. Along the border of the Pacific Ocean vast sedimentary deposits
had accumulated during the Cretaceous and Tertiary Periods. Then the
mighty upheaval came, the mountain ridge rose at the end of the Miocene
epoch and stretched itself for hundreds of miles through the region
which is now the coast of California and Oregon. Great fissures opened
in the folded crust, and floods of lava overspread an area of 150,000
square miles. A dozen dead craters show to-day where those immense
volcanic chimneys were. The depth of the lava-beds is well shown where
the Columbia River has worn its channel through. Walls of lava three
thousand feet in thickness rise on each side of the river. They are made
of columns of basalt, fitted together, like cells of a honeycomb, and
jointed, forming stone blocks laid one upon another. The lava shrinks on
cooling and forms prisms. In Ireland, the Giants' Causeway is a famous
example of basaltic formation. In Oregon, the walls of the Des Chutes
River show thirty lava layers, each made of vertical basalt columns. The
palisades of the Hudson, Mt. Tom, and Mt. Holyoke are examples on the
eastern side of the continent of basaltic rocks made by lava floods.

Northern California, northwestern Nevada, and large part of Idaho,
Montana, Oregon, and Washington are included in the basin filled with
lava at the time of the great overflow, which extended far into British
Columbia. It is probable that certain chimneys continued to discharge
until comparatively recent times. Mt. Rainier, Mt. Shasta, and Mt. Hood
are among dead volcanoes.

Quite a different history has the great Deccan lava-field of India,
which covers a larger area than the basin of our Northwest, and is in
places more than a mile in depth. It has no volcanoes, nor signs of any
ever having existed. The floods alone overspread the region, which shows
no puny "follow-up system" of scattered craters, intermittently in
eruption.

THE FIRST LIVING THINGS

Strange days and nights those must have been on the earth when the great
sea was still too hot for living things to exist in it. The land above
the water-line was bare rocks. These were rapidly being crumbled by the
action of the air, which was not the mild, pleasant air we know, but was
full of destructive gases, breathed out through cracks in the thin crust
of the earth from the heated mass below. If you stand on the edge of a
lava lake, like one of those on the islands of the Hawaiian group, the
stifling fumes that rise might make you feel as if you were back at the
beginning of the earth's history, when the solid crust was just a thin
film on an unstable sea of molten rock, and this volcano but one of the
vast number of openings by which the boiling lava and the condensed
gases found their way to the surface. Then the rivers ran black with the
waste of the rocky earth they furrowed, and there was no vegetation to
soften the bleakness of the landscape.

The beginnings of life on the earth are a mystery. Nobody can guess the
riddle. The earliest rocks were subjected to great heat. It is not
possible that life could have existed in the heated ocean or on the
land. Gradually the shores of the seas became filled up with sediment
washed down by the rivers. Layer on layer of this sediment accumulated,
and it was crumpled by pressure, and changed by heat, so that if any
plants or animals had lived along those old shores their remains would
have been utterly destroyed.

Rocks that lie in layers on top of these oldest, fire-scarred
foundations of the earth show the first faint traces of living things.
Limestone and beds of iron ore are signs of the presence of life. The
first animals and plants lived in the ancient seas.

From the traces that are left, we judge that the earliest life forms
were of the simplest kind, like some plants and animals that swim in a
drop of water. Have you ever seen a drop of pond water under a compound
microscope? It is a wonder world you look into, and you forget all the
world besides. You are one of the wonderful higher animals, the highest
on the earth. You focus on a shapeless creature that moves about and
feels and breathes, but hasn't any eyes or mouth or stomach--in fact, it
is the lowest form of animal life, and one of the smallest. It is but
one of many animal forms, all simple in structure, but able to feed and
grow and reproduce their kind.

Gaze out of the window on the garden, now. The flowering plants, the
green grass, and the trees are among the highest forms of plants. In the
drop of water under the microscope tiny specks of green are floating.
They belong to the lowest order of plants. Among the plant and the
animal forms that have been studied and named, are a few living things
the places of which in the scale are not agreed upon. Some say they are
animals; some believe they are plants. They are like both in some
respects. It is probable that the first living things were like these
confusing, minute things--not distinctly plants or animals, but the
parent forms from which, later on, both plants and animals sprang.

The lowest forms of life, plant and animal, live in water to-day. They
are tiny and their bodies are made of a soft substance like the white of
an egg. If these are at all like the living creatures that swarmed in
the early seas, no wonder they left no traces in the rocks of the early
part of the age when life is first recorded by fossils. Soft-bodied
creatures never do.

Some of the animals and the plants in the drop of water under the
microscope have body walls of definite shapes, made of lime, or of a
glassy substance called silica. When they die, these "skeletons" lie at
the bottom of the water, and do not decay, as the living part of the
body does, because they are mineral. Gradually a number of these shells,
or hard skeletons, accumulate. In a glass of pond water they are found
at the bottom, amongst the sediment. In a pond how many thousands of
these creatures must live and their shells fall to the bottom at last,
buried in the mud!

So it is easy to understand why the first creatures on earth left no
trace. The first real fossils found in the rocks are the hard shells or
skeletons of the first plants and animals that had hard parts.

AN ANCIENT BEACH AT EBB TIDE

When the tide is out, the rocks on the Maine coast have plenty of living
creatures to prove this northern shore inhabited. Starfishes lurk in the
hollows, and the tent-shaped shells of the little periwinkle encrust the
wet rocks. Mussels cling to the rocks in clumps, fastened to each other
by their ropes of coarse black hair. The furry coating of sea mosses
that encrust the rocks is a hiding-place for many kinds of living
things, some soft-bodied, some protected by shells. The shallow water is
the home of plants and animals of many different kinds. As proof of this
one finds dead shells and fragments of seaweeds strewn on the shore
after a storm.

Along the outer shores of the Cape Cod peninsula and down the Jersey
coast, the sober colouring of the shells of the north gives way to a
brighter colour scheme. In the warmer waters, life becomes gayer, if we
may judge by the rich tints that ornament the shells. The kinds of
living creatures change. They are larger and more abundant. The seaweeds
are more varied and more luxuriant in growth.

When we reach the shores of the West Indian islands and the keys of
Florida the greatest abundance and variety of living forms are found.
The submerged rocks blossom with flower-like sea anemones of every
colour. Corals, branching like trees and bushes on the sea floor, form
groves under water. Among them brilliant-hued fishes swim, and highly
ornamented shells glide, as people know who have gazed through the glass
bottoms of the boats built especially to show visitors the wonderful sea
gardens at Nassau, Bahama Islands, and at Santa Catalina Island,
southern California.

On every beach the skeletons of animals which die help to build up the
land; though the process is not so rapid in the north as on the shores
that approach the tropics. The coast of Florida has a rim of island
reefs around it built out of coral limestone. Indeed, the peninsula was
built by coral polyps. Houses in St. Augustine are built of coquina
rock, which is simply a mass of broken shells held together by a lime
cement. Every sea beach is packed with shells and other remnants of
animals and plants that live in the shallow waters. Deeper and deeper
year by year the sand buries these skeletons, and many of them are
preserved for all time.

Thus what is sandy beach to-day may, a few million years from now, be
uncovered as a ledge of sandstone with the prints of waves distinctly
shown, and fossil shells of molluscs, skeletons of fishes, and branches
of seaweed--all of them different from those then growing upon the
earth.

In the neighbourhood of Cincinnati there have been uncovered banks of
stone accumulated along the border of an ancient sea. From the sides of
granite highlands streams brought down the sand built into these oldest
sandstone rocks. The fine mud which now appears as beds of slate was the
decay of feldspar and hornblende in the same granite. Limestone beds are
full of the fossil shells of creatures that lived in the shallow seas.
Their skeletons, accumulating on the bottom, formed deep layers of
limestone mud. These rocks preserve, by the fossils they contain, a
great variety of shellfish which had limy skeletons. The sea fairly
swarmed along its shallow margin with these creatures. We might not
recognize many of the shells and other curious fossils we find in the
rock uncovered by the workmen who are cutting a railroad embankment.
They are not exactly like the living forms that grow along our beaches
to-day, but they are enough like them for us to know that they lived
along the seashore, and if we had time to examine all the rocks of this
kind preserved in a museum we should decide that seashore life was quite
as abundant then as it is now. The pressed specimens of plants of those
earliest seashores are mere imprints showing that they were pulpy and
therefore gradually decayed. Only their shape is recorded by dark stains
made by each branching part. The decay of the vegetable tissue painted
the outline on the rock which when split apart shows us what those
ancient seaweeds looked like. They belonged to the group of plants we
call kelp, or tangle, which are still common enough in the sea, though
the forms we now have are not exactly like the old ones. Seaweeds belong
to the very lowest forms of plants.

[Illustration: Crinoid from Indiana]

[Illustration: _By permission of the American Museum of Natural History_

Ammonite from Jurassic of England]

[Illustration: _By permission of the American Museum of Natural History_

Fossil corals Coquina, Hippurite limestone]

The limestones are full of fossils of corals. Indeed, there must have
been reefs like those that skirt Florida to-day built by these
lime-building polyps. Their forms are so well preserved in the rocks
that it is possible to know just how they looked when they grew in the
shallows.

One very common kind is called a cup coral, because the polyp formed a
skeleton shaped like a cup. The body wall surrounded the skeleton, and
the arms or tentacles rose from the centre of the funnel-like depression
in the top. Little cups budded off from their parents, but remained
attached, and at length the skeletons of all formed great masses of limy
rock. Some cup corals grew in a solid mass, the new generation forming
an outer layer, thus burying the parent cups.

A second type of corals in these oldest limestones is the honeycomb
group. The colonies of polyps lived in tubes which lengthened gradually,
forming compact, limy cylinders like organ pipes, fitted close together.
The living generation always inhabited the upper chambers of the tubes.
A third type is the chain coral, made of tubes joined in rows, single
file like pickets of a fence. But these walls bend into curious
patterns, so that the cross-section of a mass of them looks like a
complex pattern of crochet-work, the irregular spaces fenced with chain
stitches. Each open link is a pit in which a polyp lived.

Among the corals are sprays of a fine feathery growth embedded in the
limestone. Fine, straight, splinter-like branches are saw-toothed on one
or both edges. These limy fossils might not be seen at all, were they
not bedded in shales, which are very fine-grained. Here again are the
skeletons of animals. Each notch on each thread-like branch was the home
of a tiny animal, not unlike a sea anemone and a coral polyp.

To believe this story it is necessary only to pick up a bit of dead
shell or floating driftwood on which a feathery growth is found. These
plumes, like "sea mosses," as they are called, are not plants at all,
but colonies of polyps. Each one lived in a tiny pit, and these pits
range one above the other, so as to look like notches on the thread-like
divisions of the stem. Put a piece of this so-called "sea moss" in a
glass of sea water, and in a few moments of quiet you will see, by the
use of a magnifying glass, the spreading arms of the polyp thrust out of
each pit.

The ancient seas swarmed with these living hydrozoans, and their remains
are found preserved as fossils in the shales which once were beds of
soft mud.

The hard shells of sea urchins and starfishes are made of lime. In the
ancient seas, starfishes were rare and sea urchins did not exist, but
all over the sea bottom grew creatures called crinoids, the soft parts
of which were enclosed in limy protective cases and attached to rocks on
the sea bottom by means of jointed stems. No fossils are more plentiful
in the early limestones than these wonderful "stone lilies." Indeed, the
crinoidal limestone seemed to be built of the skeletons of these
animals. The lily-like body was flung open, as a lily opens its calyx,
when the creature was feeding. But any alarm caused the tentacles to be
drawn in, and the petal-like divisions of the body wall to close tightly
together, till that wall looked like an unopened bud.

On the bottom of the Atlantic, near the Bahama Islands, these stone
lilies are still found growing. Their jointed stems and body parts are
as graceful in form and motion as any lily. The creature's mouth is in
the centre of the flower-like top, and it feeds like the sea urchin, on
particles obtained in the sea water.

The old limestones contain great quantities of "lamp shells," which are
old-fashioned bivalves. Their shells remind us of our bivalve clams and
scallops, but the internal parts were very different. The gills of clams
and oysters are soft parts. Inside of the lamp shells are coiled, bony
arms, supporting the fringed gills.

It is fortunate for us that a few lamp shells still live in the seas. By
studying the soft parts of these living remnants of a very old race we
can know the secrets of the lives of those ancient lamp shells, the
soft parts of which were all washed away, and the fossil shells of which
are preserved. Gradually the lamp shells died out, and the modern
bivalves have come to take their places. Just so, the ancient crinoids
are now almost extinct; the sea urchins and the starfishes have
succeeded them.

The chambered nautilus has its shell divided by partitions and it lives
in the outer chamber, a many-tentacled creature, that is a close
relative of the soft-bodied squid. In the ancient seas the same family
was represented by huge creatures the shells of which were chambered,
but not coiled. Their abundance and great size are proved by the rocks
in which their fossils are preserved. Some of them must have been the
rulers of the sea, as sharks and whales are to-day. Fossil specimens
have been found more than fifteen feet long and ten inches in diameter
in the ancient rocks of some of the Western States. It is possible to
read from the lowest rock formations upward, the rise of these sea
giants and their gradual decline. Certain strata of limestone contain
the last relics of this race, after which they became extinct. As the
straight-chambered forms diminished, great coiled forms became more
abundant, but all died out.

One of the most abundant fossil animals in ancient rocks is called a
trilobite. Its body is divided by two grooves into three parts, a
central ridge extending the whole length of the body and two side
ridges. The front portion of the shell formed the head shield, and
behind the main body part was a little tail shield. The skeleton was
formed of many movable jointed plates, and the creature had eyes set in
the head shield just as the king crab's are set. Jointed legs in pairs
fringed each side of the body. Each leg had two branches, one for
walking, the other for swimming. A pair of feelers rose from the head.
The body could be rolled into a ball when danger threatened, by bringing
head and tail together.

These remarkable, extinct trilobites were the first crustaceans. Their
nearest living relative to-day is the horseshoe crab. The fresh-water
crayfish and the lobster are more distant relatives: so are the shrimps
and the prawns. No such abundance of these creatures exists to-day as
existed when the trilobites thronged the shallows. So well preserved are
these skeletons that, although there are no living trilobites for
comparison, it is possible to find out from the fossil enough about
their structure to know how they fed and lived their lives along with
the straight-horns which were the scavengers of those early seas and the
terror of smaller creatures. The trilobites throve, and, dying, left
their record in the rocks; then disappeared entirely. We find their
fossils in a great variety of forms, shapes, and sizes. The smallest is
but a fraction of an inch long, the largest twenty inches long.

The ancient rocks, in which these lower forms of life have left their
fossils, are known as the Silurian system. The time in which these rocks
were accumulating under the seas covers a vast period. We call it the
Age of Invertebrates, because these soft-bodied, hard-shelled animals,
the crinoids, the molluscs, and the trilobites, with bony external
skeletons and no backbones, were the most abundant. They overshadowed
all other forms of life. The rocks of this wonderful series were formed
on the shores of a great inland sea that covered the central portion of
North America. In the ages that followed, these rocks were covered
deeply with later sediments. But the upheavals of the crust have broken
open and erosion has uncovered these strata in different regions.
Geologists have found written there, page upon page, the record of life
as it existed in the early seas.

THE LIME ROCKS

"Hard" water and "soft" water are very different. The rain that falls
and fills our cisterns is not softer or more delightful to use than the
well water in some favoured regions. In it, soap makes beautiful, creamy
suds, and it is a real pleasure to put one's hands into it. But in hard
water soap seems to curdle, and some softening agent like borax has to
be added or the water will chap the hands. There is little satisfaction
in using water of this kind for any purpose.

Hard water was as soft as any when it fell from the sky; but the rain
water trickled into the ground and passed through rocks containing lime.
Some of this mineral was absorbed, for lime is readily soluble in water.
Clear though it may be, water that has lime in it has quite a different
feeling from rain water. Blow the breath into a basin of hard water, and
a milky appearance will be noted. The carbonic acid gas exhaled from the
lungs unites with the invisible lime, causing it to become visible
particles of carbonate of lime, which fall to the bottom of the basin.

Nearly all well water is hard. So is the water of lakes and rivers and
the ocean, for limestone is one of the most widely distributed rocks in
the surface of the earth. Rain water makes its way into the earth's
crust, absorbs mineral substances, and collects in springs which feed
brooks and rivers and lakes. Wells are holes in the ground which bore
into water-soaked strata of sand.

We gain something from the lime dissolved in hard water, for it is an
essential part of our food. We must drink a certain amount of water each
day to keep the body in perfect health. The lime in this water goes
chiefly to the building of our bones. Plant roots take up lime in the
water that mounts as sap through the plant bodies. We get some of the
lime we need in vegetable foods we eat.

All of the kingdom of vertebrate animals, from the lowest forms to the
highest, all of the shell-bearing animals of sea and land, require lime.
Many of the lower creatures especially these in the sea, such as corals
and their near relatives, encase themselves in body walls of lime. They
absorb the lime from the sea water, and deposit it as unconsciously as
we build the bony framework of our bodies.

All the bone and shell-bearing creatures that die on the earth and in
the sea restore to the land and to the water the lime taken by the
creatures while they lived. Carbonic acid gas in the water greatly
hastens the dissolving of dead shells. Carbonic acid gas, whether free
in the air, or absorbed by percolating water, hastens the dissolving of
skeletons of creatures that die upon land. Then the raw materials are
built again into lime rocks underground.

The lime rocks are the most important group in the list of rocks that
form the crust of the earth. They are made of the elements calcium,
carbon, and oxygen, yet the different members of this calcite group
differ widely in composition and appearance. So do oyster shells and
beef bones, though both contain quantities of carbonate of lime.

Calcite is a soft mineral, light in weight, sometimes white, but oftener
of some other colour. It may be found crystallized or not. Whenever a
drop of acid touches it, a frothy effervescence occurs. The drop of acid
boils up and gives off the pungent odour of carbonic acid gas.

The reason that calcite is hard to find in rocks is that percolating
water, charged with acids, is constantly stealing it, and carrying it
away into the ocean. The rocks that contain it crumble because the limy
portions have been dissolved out.

Some limestones resist the destructive action of water. When they are
impregnated with silica they become transformed into marble, which takes
a high polish like granite. Acids must be strong to make any impression
on marble.

The thick beds of pure limestone that underlie the surface soil in
Kentucky and in parts of Virginia sometimes measure several hundred feet
in thickness, a single stratum often being twenty feet thick. They are
all horizontal, for they were formed on sea bottom, and have not been
crumpled in later time. The dead bodies of sea creatures contributed
their shells and skeletons to the lime deposit on the sea bottom. Who
can estimate the time it took to form those thick, solid layers of lime
rock? The animals were corals, crinoids, and molluscs. Little sand and
clay show in the lime rock of this period, before the marshes of the
Carboniferous Age took the place of the ancient inland sea of the
Subcarboniferous Period, the sedimentary accumulations of which we are
now talking about.

The living corals one sees in the shallow water of the Florida coast
to-day are building land by building up their limy skeletons. The reefs
are the dead skeletons of past generations of these tiny living things.
They take in lime from the water, and use it as we use lime in building
our bones. In each case it is an unconscious process of animal
growth--not a "building process" like a mason's building of a wall. Many
people think that the coral polyp builds in this way. They give it
credit for patience in a great undertaking. All the polyp does is to
feed on whatever the water supplies that its digestive organs can use.
It is like a sea anemone in appearance and in habits of life. It is not
at all like an insect. Yet it is common to hear people speak of the
"coral insect"! Do not let any one ever hear you repeat such a mistake.

Southern Florida is made out of coral rock, but thinly covered with
soil. It was made by the growth of reef after reef, and it is still
growing.

The Cretaceous Period of the earth's eventful history is named for the
lime rock which we know as chalk. Beds of this recent kind of limestone
are found in England and in France, pure white, made of the skeletons of
the smallest of lime-consuming creatures, Foraminifera. They swarmed in
deep water, and so did minute sponge animalcules and plant forms called
Diatoms that took silica from the water, and formed their hard parts of
this glassy substance. The result is seen in the nodules of flint found
in the soft, snow-white chalk. Did you ever use a piece of chalk that
scratched the black-board? The flint did it. Have you ever seen the
chalk cliffs of Dover? When you do see them, notice how they gleam white
in the sun. See how the rains have sculptured those cliffs. The
prominences left standing out are strengthened by the flint they
contain. Chalk beds occur in Texas and under our great plains; but the
principal rocks of the age in America were sandstones and clays.

THE AGE OF FISHES

The first animal with a backbone recorded its existence among the
fossils found in rocks of the upper Silurian strata. It is a fish; but
the earliest fossils are very incomplete specimens. We know that these
old-fashioned fishes were somewhat like the sturgeons of our rivers.
Their bodies were encased in bony armour of hard scales, coated with
enamel. The bones of the spine were connected by ball and socket joints,
and the heads were movable. In these two particulars the fishes
resembled reptiles. The modern gar-pike has a number of the same
characteristics.

Another backboned creature of the ancient seas was the ancestral type of
the shark family. In some points this old-fashioned shark reminds us of
birds and turtles. These early fishes foreshadowed all later
vertebrates, not yet on the earth. After them came the amphibians, then
the reptiles, then the birds, and latest the mammals.

The race of fishes began, no doubt, with forms so soft-boned that no
fossil traces are preserved in the rocks. When those with harder bones
appeared, the fossil record began, and it tells the story of the passing
of the early, unfish-like forms, and the coming of new kinds, great in
size and in numbers, that swarmed in the seas, and were tyrants over all
other living things. They conquered the giant straight-horns and
trilobites, former rulers of the seas.

[Illustration: _By permission of the American Museum of Natural History_

A sixteen-foot fossil fish from Cretaceous of Kansas, with a modern
tarpon]

[Illustration: _By permission of the American Museum of Natural History_

Cañon Diablo meteorite from Arizona]

One of these giant fishes fifteen to twenty feet long, three feet wide,
had jaws two feet long, set with blade-like teeth. Devonian rocks in
Ohio have yielded fine fossils of gigantic fishes and sharks.

Devonian fishes were unlike modern kinds in these particulars, the
spinal column extended to the end of the tail, whether the fins were
arranged equally or unequally on the sides; the paired side fins look
like limbs fringed with fins. Every Devonian fish of the gar type seems
to have had a lung to help out its gill-breathing.

In these traits the first fishes were much like the amphibians. They
were the parent stock from which branched later the true fishes and the
amphibians, as a single trunk parts into two main boughs. The trunk is
the connecting link.

The sea bottom was still thronged with crinoids, and lamp shells, and
cup corals. Shells of both clam and snail shapes are plentiful. The
chambered straight-horns are fewer and smaller, and coiled forms of this
type of shell are found. Trilobite forms are smaller, and their numbers
decrease.

The first land plants appeared during this age. Ferns and giant club
mosses and cycads grew in swampy ground. This was the beginning of the
wonderful fern forests that marked the next age, when coal was formed.

The rocks that bear the record of these living things in their fossils,
form strata of great thickness that overlie the Silurian deposits. There
is no break between them. So we understand that the sea changed its
shore-line only when the Silurian deposits rose to the water-level.

The Devonian sea was smaller than the Silurian. A great tract of
Devonian deposits occupies the lower half of the state of New York,
Canada between Lakes Erie and Huron, and the northern portions of
Indiana and Illinois. These older layers of the stratified rock are
covered with the deposits of later periods. Rivers that cut deep
channels reveal the earlier rocks as outcrops along their canyon walk.
The record of the age of fishes is, for the most part, still an unopened
book. The pages are sealed, waiting for the geologist with his hammer to
disclose the mysteries.

KING COAL

In this country, and in this age, who can doubt that coal is king? It is
one of the few necessities of life. In various sections of the country,
layers of coal have been discovered--some near the surface, others deep
underground. These are the storehouses of fuel which the coal miners dig
out and bring to the surface, and the railroads distribute. From
Pennsylvania and Ohio to Alabama stretches the richest coal-basin.
Illinois and Indiana contain another. From Iowa southward to Texas
another broad basin lies. Central Michigan and Nova Scotia each has
isolated coal-basins. All these have been discovered and mined, for they
lie in the oldest part of the country.

In the West, coal-beds have been discovered in several states, but many
regions have not yet been explored. Vast coal-fields, still untouched,
have been located in Alaska. The Government is trying to save this fuel
supply for coming generations. Many of the richest coal-beds from Nova
Scotia southward dip under the ocean. They have been robbed by the
erosive action of waves and running water. Glaciers have ground away
their substance, and given it to the sea. Much that remains intact must
be left by miners on account of the difficulties of getting out coal
from tilted and contorted strata.

As a rule, the first-formed coal is the best. The Western coal-fields
belong to the period following the Carboniferous Age. Although
conditions were favourable to abundant coal formation, Western coal is
not equal to the older, Eastern coal. It is often called _lignite_, a
word that designates its immaturity compared with anthracite.

Coal formed in the Triassic Period is found in a basin near Richmond,
Virginia. There is an abundance of this coal, but it has been subjected
to mountain-making pressure and heat, and is extremely inflammable. The
miners are in constant danger on account of coal gas, which becomes
explosive when the air of the shaft reaches and mingles with it. This
the miner calls "fire damp." North Carolina has coal of the same
formation, that is also dangerous to mine, and very awkward to reach, on
account of the crumpling of the strata.

There are beds of coal so pure that very little ash remains after the
burning. Five per cent, of ash may be reasonably expected in pure coal,
unmixed with sedimentary deposits. Such coal was formed in that part of
the swamp which was not stirred by the inflow of a river. Wherever muddy
water flowed in among the fallen stems of plants, or sand drifted over
the accumulated peat, these deposits remained, to appear later and
bother those who attempt to burn the coal.

[Illustration: Eocene fish]

[Illustration: _By permission of the American Museum of Natural History_

Trilobite from the Niagara limestone, Upper Silurian, of Western New
York]

[Illustration: Sigillaria, Stigmaria and Lepidodendron]

[Illustration: _By permission of the American Museum of Natural History_

Coal fern]

You know pure coal, that burns with great heat and leaves but little
ashes. You know also the other kind, that ignites with difficulty, burns
with little flame, gives out little heat, and dying leaves the furnace
full of ashes. You are trying to burn ancient mud that has but a small
proportion of coal mixed with it. The miners know good coal from poor,
and so do the coal dealers. It is not profitable to mine the impure part
of the vein. It costs as much to mine and ship as the best quality, and
it brings a much lower price.

The deeper beds of coal are better than those formed in comparatively
recent time and found lying nearer the surface. In many bogs a layer of
embedded root fibres, called peat, is cut into bricks and dried for
burning. Deeper than peat-beds lie the _lignites_, which are old beds of
peat, on the way to become coal. _Soft coal_ is older than lignite. It
contains thirty to fifty per cent. of volatile matter, and burns
readily, with a bright blaze. The richest of this bituminous coal is
called _fat_, or _fusing coal_. The bitumen oozes out, and the coal
cakes in burning. Ordinary soft coal contains less, but still we can see
the resinous bitumen frying out of it as it burns. There is more heat
and less volatile matter in _steam coal_, so-called because it is the
fuel that most quickly forms steam in an engine. _Hard coal_ contains
but five to ten per cent. of volatile matter. It is slow to ignite and
burns with a small blue blaze.

From peat to anthracite coal I have named the series which increases
gradually in the amount of heat it gives out, and increases and then
decreases in its readiness to burn and in the brightness of its flame.
Anthracite coal has the highest amount of fixed carbon. This is the
reason why it makes the best fuel, for fixed carbon is the substance
which holds the store of imprisoned sunlight, liberated as heat when the
coal burns. Tremendous pressure and heat due to shrinking of the earth's
crust have crumpled and twisted the strata containing coal in eastern
Pennsylvania, and thus changed bituminous coal into anthracite. Ohio
beds, formed at the same time, but undisturbed by heat and pressure, are
bituminous yet.

The coal-beds of Rhode Island are anthracite, but the coal is so hard
that it will not burn in an open fire. The terrible, mountain-making
forces that crumpled these strata and robbed the coal of its volatile
matter, left so little of the gas-forming element, that a very special
treatment is necessary to make the carbon burn. It is used successfully
in furnaces built for the smelting of ores.

The last stage in the coal series is a black substance which we know as
black lead, or graphite. We write with it when we use a "lead" pencil.
This is anthracite coal after all of the volatile matter has been driven
out of it. It cannot burn, although it is solid carbon. The beds of
graphite have been formed out of coal by the same changes in the
earth's crust which have converted soft coal into anthracite.

The tremendous pressure that bears on the coal measures has changed a
part of the carbon into liquid and gaseous form. Lakes of oil have been
tapped from which jets of great force have spouted out. Such
accumulations of oil usually fill porous layers of sandstone and are
confined by overlying and underlying beds of impervious clay. Gas may be
similarly confined until a well is drilled, relieving the pressure, and
furnishing abundant or scanty supply of this valuable fuel. Western
Pennsylvania coal-fields have beds of gas and oil. If mountain-making
forces had broken the strata, as in eastern Pennsylvania, the gas and
the oil would have been lost by evaporation.

This is what happened in the anthracite coal-belt.

HOW COAL WAS MADE

The broad, rounded dome of a maple tree shades my windows from the
intense heat of this August day. The air is hot, and every leaf of the
tree's thatched roof is spread to catch the sunlight. The carbon in the
air is breathed in through openings on the under side of each leaf. The
sap in the leaf pulp uses the carbon in making starch. The sun's heat is
absorbed. It is the energy that enables the leaf-green to produce a
wonderful chemical change. Out of soil water, brought up from the roots,
and the carbonic acid gas, taken in from the air, rich, sugary starch is
manufactured in the leaf laboratory.

This plant food returns in a slow current, feeding the growing cells
under the bark, from leaf tip to root tip, throughout the growing tree.
The sap builds solid wood. The maple tree has been built out of muddy
water and carbon gas. It stands a miracle before our eyes. In its tough
wood fibres is locked up all the heat its leaves absorbed from the sun,
since the day the maple seed sprouted and the first pair of leaves
lifted their palms above the ground.

If my maple tree should die, and fall, and lie undisturbed on the
ground, it would slowly decay. The carbon of its solid frame would pass
back into the air, as gas, and the heat would escape so gradually that I
could not notice it at all, unless I thrust my hand into the warm,
crumbling mass.

If my tree should be cut down to-day and chopped into stove wood, it
would keep a fire in my grate for many months.

Burning destroys wood substance a great deal faster than decay in the
open air does, but the processes of rotting and burning are alike in
this: each process releases the carbon, and gives it back to the air. It
gives back also the sun's heat, stored while the tree was growing. There
is left on the ground, and in the ashes on the hearth, only the mineral
substance taken up in the water the roots gathered underground.

If my tree stood in swampy ground and fell over under a high wind, the
water that covered it and saturated its substance would prevent decay.
The carbon would not be allowed to escape as a gas to the air; the woody
substance would become gradually changed into _peat_. In this form it
might remain for thousands of years, and finally be changed into coal.

Whether it was burned while yet in the condition of peat, or millions of
years later, when it was transformed into coal, the heat stored in its
substance was liberated by the burning. The carbon and the heat went
back to the air.

Every green plant we see spreads its leaves to the sun. Every stick of
wood we burn, and every lump of coal, is giving back, in the form of
light and heat, the energy that came from sunshine and was captured by
the green leaves. How long the wood has held this store of heat we may
easily compute, for we can read the age of a tree. But the age of coal
we cannot accurately state. The years probably should be counted by
millions, instead of thousands.

The great inland sea that covered the middle portion of the continent
during the Silurian and the Devonian periods, became shallow by the
deposit of vast quantities of sediment. Along the lines of the deposits
of greatest thickness, a crumpling of the earth's crust lifted the first
fold of the Alleghany Mountains as a great sea wall on the east, and on
the western shore another formed the beginning of the Ozark Mountain
system in Missouri. An island was lifted out of the sea, forming the
elevated ground on which the city of Cincinnati now stands. Various
other ridges and islands divided the ancient sea into much smaller
bodies of water. Hemmed in by land these shallow sea-basins gradually
changed into fresh-water lakes, for they no longer had connection with
the ocean, and all the water they received came from rain. After
centuries of freshets, and of filling in with the rock débris brought by
the streams, they became great marshes, in which grew water-loving
plants. Generation after generation of these plants died, and their
remains, submerged by the water, were converted into peat. In the
course of ages this peat became coal. This is the history of the coal
measures.

There is no guesswork here. The stems of plants do not lose their
microscopic structure in all the ages it has taken to transform them to
coal. A thin section of coal shows under a magnifier the structure of
the stems of the coal-forming plants. Moreover, the veins of coal
preserve above or below them, in shales that were once deposits of mud,
the branching trunks of trees, perfectly fossilized. There are no better
proofs of the vegetable origin of coal than the lumps themselves. But
they are plain to the naked eye, while the coal tells its story to the
man with the microscope.

The fossil remains of the plants that flourished when coal was forming
are gigantic, compared with plants of the same families now living. We
must conclude that the climate was tropical, the air very heavy with
moisture, and charged much more heavily than it is now with carbonic
acid gas.

These conditions produced, in rapid succession, forests of tree ferns
and horsetails and giant club mosses. These are the three types of
plants out of which the coal was made. They were all rich in resin,
which makes the coal burn readily. The ferns had stems as large as tree
trunks. Some have been found that are eighteen inches in diameter. We
know they are ferns, because the leaves are found with their fruits
attached to them in the manner of present-day ferns. The stems show the
well known scar by which fern leaves are joined. And the wood of these
fossil fern stems is tubular in structure, just as the wood of living
ferns is to-day.

Among the ferns which dominated these old marsh forests grew one kind,
the scaly leaves of which covered the stems and bore their fruits on the
branching tips. These giants, some of them with trunks four feet in
diameter, belong to the same group of plants as our creeping club
mosses, but in the ancient days they stood up among the other ferns as
trees forty or fifty feet high.

The giant scouring rushes, or horsetails, had the same general
characteristics as the little reed-like plants we know by those names
to-day.

The highest plants of the coal period were leafy trees with nut-like
fruits, that resemble the yew trees of the present. These gigantic trees
were the first conifers upon the earth. They foreshadowed the pines and
the other cone-bearing evergreens. Their leaves were broad and their
fruits nut-like. The Japanese ginkgo, or maidenhair fern tree, is an
old-fashioned conifer somewhat like those first examples of this family.
Trunks sixty to seventy feet long, crowned with broad leaves and a spike
of fruit, have been found lying in the upper layers of the coal-seams,
and in sandstone strata that lie between the strata of coal. Peculiar
circular discs, which the microscope reveals along the sides of the wood
fibres of these fossil trees, prove the wood structure to be like that
of modern conifers.

Generation after generation of forests lived and died in the vast
spreading swamps of this era. The land sank, and freshets came here and
there, drowning out all plant life, and covering the layers of peat with
beds of sand or mud. When the water went down, other forests took
possession, and a new coal-bed was started. It is plainly seen that
flooding often put an end to coal formation. Fifteen seams of coal, one
above another, is the greatest number that have been found. The veins
vary from one inch to forty feet in thickness. These are separated by
layers of sandstone or shale, which accumulated as sediment, covering
the stumps of dead tree ferns and other growths, and preserving them as
fossils to tell the story of those bygone ages as plainly as any other
record could have done.

Fresh-water animals succeeded those of salt water in the swamps that
formed the coal measures. Overhead, the first insects flitted among the
branches of the tree ferns. Dragon-flies darted above the surface and
dipped in water as they do to-day. Spiders, scorpions, and cockroaches,
all air-breathing insects, were represented, but none of the higher,
nectar-loving insects, like flies and bees and butterflies, were there.
Flowering plants had not yet appeared on the earth. Snakelike
amphibians, some fishlike, some lizard-like, and huge crocodilian forms
appeared for the first time. These air-breathing swamp-dwellers could
not have lived in salt water.

Fresh-water molluscs and land shells appear for the first time as
fossils in the rocks of the coal measures. On the shores of the ocean,
the rocks of this period show that trilobites, horseshoe crabs, and
fishes still lived in vast numbers, and corals continued to form
limestone. The old types of marine animals changed gradually, but the
coal measures show strikingly different fossils. These rocks bear the
first record of fresh-water and land animals.

THE MOST USEFUL METAL

It is fortunate for us all that, out of the half-dozen so-called useful
metals, iron, which is the most useful of them all to the human race,
should be also the most plentiful and the cheapest. Aluminum is abundant
in the common clay and soil under our feet. But separating it is still
an expensive process; so that this metal is not commercially so
plentiful as iron is, nor is it cheap.

All we know of the earth's substance is based on studies of the
superficial part of its crust, a mere film compared with the eight
thousand miles of its diameter. Nobody knows what the core of the
earth--the great globe under this surface film--is made of; but we know
that it is of heavier material than the surface layer; and geologists
believe that iron is an important element in the central mass of the
globe.

One thing that makes this guess seem reasonable is the great abundance
of iron in the earth's crust. Another thing is that meteors which fall
on the earth out of the sky prove to be chiefly composed of iron. All of
their other elements are ones which are found in our own rocks. If we
believe that the earth itself is a fragment of the sun, thrown off in a
heated condition and cooling as it flew through space, we may consider
it a giant meteor, made of the substances we find in the chance meteor
that strikes the earth.

Iron is found, not only in the soil, but in all plant and animal bodies
that take their food from the soil. The red colour in fruits and
flowers, and in the blood of the higher animals, is a form in which iron
is familiar to us. It does more, perhaps, to make the world beautiful
than any other mineral element known.

But long before these benefits were understood, iron was the backbone of
civilization. It is so to-day. Iron, transformed by a simple process
into steel, sustains the commercial supremacy of the great civilized
nations of the world. The railroad train, the steel-armoured battleship,
the great bridge, the towering sky-scraper, the keen-edged tool, the
delicate mechanism of watches and a thousand other scientific
instruments--all these things are possible to-day because iron was
discovered and has been put to use.

It was probably one of the cave men, poking about in his fire among the
rocks, who discovered a lump of molten metal which the heat had
separated from the rest of the rocks. He examined this "clinker" after
it cooled, and it interested him. It was a new discovery. It may have
been he, or possibly his descendants, who learned that this metal could
be pounded into other shapes, and freed by pounding from the pebbles
and other impurities that clung to it when it cooled. The relics of
iron-tipped spears and arrows show the skill and ingenuity of our early
ancestors in making use of iron as a means of killing their prey. The
earliest remains of this kind have probably been lost because the iron
rusted away.

Man was pretty well along on the road to civilization before he learned
where iron could be found in beds, and how it could be purified for his
use. We now know that certain very minute plants, which live in quiet
water, cause iron brought into that water to be precipitated, and to
accumulate in the bottom of these boggy pools. In ancient days these bog
deposits of iron often alternated with coal layers. Millions of years
have passed since these two useful substances were laid down. To-day the
coal is dug, along with the bog iron. The coal is burned to melt the
iron ore and prepare it for use. It is a fortunate region that produces
both coal and iron.

Bituminous coal is plentiful, and scattered all over the country, while
anthracite is scarce. The cheapest iron is made in Alabama, which has
its ore in rich deposits in hillsides, and coal measures close by,
furnishing the raw material for coke. The result is that the region of
Birmingham has become the centre of great wealth through the development
of iron and coal mines.

Where water flows over limestone rock, and percolates through layers of
this very common mineral, it causes the iron, gathered in these rock
masses, to be deposited in pockets. All along the Appalachian Mountains
the iron has been gathered in beds which are being mined. These beds of
ore are usually mixed with clay and other earthy substances from which
the metal can be separated only by melting. The ore is thrown into a
furnace where the metal melts and trickles down, leaving behind the
non-metallic impurities. It is drawn off and run into moulds, where it
cools in the form of "pig" iron.

The first fuel used in the making of pig iron from the ore was charcoal.
In America the early settlers had no difficulty in finding plenty of
wood. Indeed, the forests were weeds that had to be cut down and burned
to make room for fields of grain. The finding of iron ore always started
a small industry in a colony. If there was a blacksmith, or any one else
among the small company who understood working in iron, he was put in
charge.

To make the charcoal, wood was cut and piled closely in a dome-shaped
heap, which was tightly covered with sods, except for a small opening
near the ground. In this a fire was built, and smothered, but kept going
until all the wood within the oven was charred.

This fuel burned readily, with an intense heat, and without ashes.
Sticks of charcoal have the form of the wood, and they are stiff enough
to hold up the ore of iron so that it cannot crush out the fire. For a
long time American iron was supplied by little smelters, scattered here
and there. The workmen beat the melted metal on the forge, freeing it
from impurities, and shaping the pure metal into useful articles.
Sometimes they made it into steel, by a process learned in the Old
World.

The American iron industry, which now is one of the greatest in the
world, centres in Pittsburg, near which great deposits of iron and coal
lie close together. The making of coke from coal has replaced the
burning of charcoal for fuel. When the forests were cut away by
lumbermen, the supply of charcoal threatened to give out, and
experiments were made in charring coal, which resulted in the successful
making of coke, a fuel made from coal by a process similar to the making
of charcoal from wood. The story of the making of coke out of hard and
soft coal is a long one, for it began as far back as the beginning of
the nineteenth century.

In 1812 the first boat-load of anthracite coal was sent to Philadelphia
from a little settlement along the Lehigh River. A mine had been opened,
the owner of which believed that the black, shiny "rocks" would burn.
His neighbours laughed at him, for they had tried building fires with
them, and concluded that it could not be done. In Philadelphia, the
owners of some coke furnaces gave the new fuel a trial, in spite of the
disgust of the stokers, who thought they were putting out their fires
with a pile of stones. After a little, however, the new fuel began to
burn with the peculiar pale flame and intense heat that we know so
well, and the stokers were convinced that here was a new fuel, with
possibilities in it.

But it was hard for people to be patient with the slow starting of this
hard coal. Not until 1840 did it come into general favour, following the
discovery that if hot air was supplied at the draught, instead of cold,
anthracite coal became a perfect fuel.

At Connellsville, Pennsylvania, a vein of coal was discovered which made
coke of the very finest quality. Around this remarkable centre, coke
ovens were built, and iron ore was shipped in, even from the rich beds
of the Lake Superior country. But it was plain to see that Connellsville
coal would become exhausted; and so experiments in coke-making from
other coals were still made. When soft coal burns, a waxy tar oozes out
of it, which tends to smother the fire. Early experiments with coal in
melting iron ore indicated that soft coal was useless as a substitute
for charcoal and coke; but later experiments proved that coke of fine
quality can be made out of this bituminous soft coal, by drawing off the
tar which makes the trouble. New processes were invented by which
valuable gas and coal tar are taken out of bituminous coal, leaving, as
a residue, coke that is equal in quality to that made from the
Connellsville coal. Fortunes have been made out of the separation of the
elements of the once despised soft coal. For the coke and each of its
by-products, coal tar and coal gas, are commercial necessities of life.

The impurities absorbed by the melting iron ore include carbon,
phosphorus, and silicon. Carbon is the chief cause of the brittleness of
cast iron. The puddling furnace was invented to remove this trouble. The
melted ore was stirred on a broad, basin-like hearth, with a
long-handled puddling rake. The flames swept over the surface, burning
the carbon liberated by the stirring. It was a hard, hot job for the man
at the rake, but it produced forge iron, that could be shaped, hot or
cold, on the anvil.

The next improvement was the process of pressing the hot iron between
grooved rollers to rid it of slag and other foreign matters collected in
the furnace. The old way was to hammer the metal free from such
impurities. This was slow and hard work.

Iron was an expensive and scarce metal until the hot blast-furnace
cheapened the process of smelting the ore. The puddling furnace and the
grooved rollers did still more to bring it into general use. The
railroads developed with the iron industry. Soon they required a metal
stronger than iron. Steel was far too expensive, though it was just what
was needed. Efforts were made to find a cheap way to change iron into
steel. Sir Henry Bessemer solved the problem by inventing the Bessemer
converter. It is a great closed retort, which is filled with melted pig
iron. A draught admits air, and the carbon is all burned out. Then a
definite amount of carbon, just the amount required to change iron into
steel, is added, by throwing in bars of an alloy of carbon and
manganese. The latter gives steel its toughness, and enables it to
resist greater heat without crystallizing and thus losing its temper.

When the carbon has been put in, the retort is closed. The molten metal
absorbs the alloy, and the product is Bessemer steel. In fifteen minutes
pig iron can be transformed into ingot steel. The invention made
possible the use of steel in the construction of bridges, high
buildings, and ships. It made this age of the world the Age of Steel.

THE AGE OF REPTILES

Two big and interesting reptiles we see in the Zoo, the crocodile and
its cousin, the alligator. In the everglades of Florida both are found.
The crocodile of the Nile is protected by popular superstition, so it is
in better luck than ours. The alligators have been killed off for their
skins, and it is only a matter of time till these lumbering creatures
will be found only in places where they are protected as the remnants of
a vanished race. Giant reptiles of other kinds are few upon the earth
now. The _boa constrictor_ is the giant among snakes. The great tropical
turtles represent an allied group. Most of the turtles, lizards, and
snakes are small, and in no sense dominant over other creatures.

The rocks that lie among the coal measures contain fossils of huge
animals that lived in fresh water and on land, the ancestors of our
frogs, toads, and salamanders, a group we call amphibians. Some of these
animals had the form of snakes; some were fishlike, with scaly bodies;
others were lizard-like or like huge crocodiles. These were the
ancestors of the reptiles, which became the rulers of land and sea
during the Mesozoic Era. The rocks that overlie the coal measures
contain fossils of these gigantic animals.

Strange crocodile-like reptiles, with turtle-like beaks and tusks, but
no teeth, left their skeletons in the mud of the shores they frequented.
And others had teeth in groups--grinders, tearers, and cutters--like
mammals. These had other traits like the old-fashioned, egg-laying
mammals, the duck-billed platypus, for example, that is still found in
Australia. Along with the remains of these creatures are found small
pouched mammals, of the kangaroo kind, in the rocks of Europe and
America. These land animals saw squatty cycads, and cone-bearing trees,
the ancestors of our evergreens, growing in forests, and marshes covered
with luxuriant growths of tree ferns and horsetails, the fallen bodies
of which formed the recent coal that is now dug in Virginia and North
Carolina. Ammonites, giant sea snails, with chambered shells that
reached a yard and more in diameter, and gigantic squids, swam the seas.
Sea urchins, starfish, and oysters were abundant. Insects flitted
through the air, but no birds appeared among the trees or beasts in the
jungles. Over all forms of living creatures reptiles ruled. They were
remarkable in size and numbers. There were swimming, running, and flying
forms.

[Illustration: Banded sandstone from Calico Cañon, South Dakota]

[Illustration: _By permission of the American Museum of Natural History_

Opalized wood from Utah]

[Illustration: _By permission of the American Museum of Natural History_

Restoration of a carnivorous Dinosaur, Allosaurus, from the Upper
Jurassic and Lower Cretaceous of Wyoming. When erect the animal was
about 15 feet high]

The fish-reptile, _Ichthyosaurus_, was a hump-backed creature, thirty to
forty feet long, with short neck, very large head, and long jaw, set
with hundreds of pointed teeth. Its eye sockets were a foot across. The
four short limbs were strong paddles, used for swimming. The long,
slender tail ended in a flat fin. Perfect skeletons of this creature
have been found. Its rival in the sea was the lizard-like
_Plesiosaurus_, the small head of which was mounted on a long neck. The
tail was short, but the paddles were long and powerful. No doubt this
agile creature held its own, though somewhat smaller than the more
massively built Ichthyosaurus.

The land reptiles called _Dinosaurs_ were the largest creatures that
have ever walked the earth. In the American Museum of Natural History,
in New York, the mounted skeleton of the giant Dinosaur fairly takes
one's breath away. It is sixty-six feet long, and correspondingly large
in every part, except its head. This massive creature was remarkably
short of brains.

The strangest thing about the land reptiles is the fact that certain of
them walked on their hind legs, like birds, and made three-toed tracks
in the mud. Indeed, these fossil tracks, found in slate, were called
bird tracks, until the bones of the reptile skeleton with the bird-like
foot were discovered. Certain long grooves in the slate, hitherto
unexplained, were made by the long tail that dragged in the mud.

When the mud dried, and was later covered with sediment of another kind,
these prints were preserved, and when the bed of rock was discovered by
quarrymen, the two kinds split apart, showing the record of the stroll
of a giant along the river bank in bygone days.

The flying reptiles were still more bird-like in structure, though
gigantic in size. Imagine the appearance of a great lizard with
bat-like, webbed wings and bat-like, toothed jaws! The first feathered
fossil bird was discovered in the limestone rock of Bavaria. It was a
wonderfully preserved fossil, showing the feathers perfectly. Three
fingers of each "hand" were free and clawed, so that the creature could
seize its prey, and yet use its feathered wings in flight. The small
head had jaws set with socketed teeth, like a reptile's, and the long,
lizard tail of twenty-one bones had a pair of side feathers at each
joint. This _Archeopteryx_ is the reptilian ancestor of birds. During
this age of the world, one branch of the reptile group established the
family line of birds. The bird-like reptiles are the connecting link
between the two races. How much both birds and reptiles have changed
from that ancient type, their common ancestor!

I have mentioned but a few of the types of animals that make the
reptilian age the wonder of all time. One after another skeletons are
unearthed and new species are found. The Connecticut River Valley, with
its red sandstones and shales of the Mesozoic Era, is famous among
geologists, because it preserves the tracks of reptiles, insects, and
crustaceans. These signs tell much of the life that existed when these
flakes of stone were sandy and muddy stretches Not many bones have been
found, however. The thickness of these rocks is between one and two
miles. The time required to accumulate so much sediment must have been
very great.

[Illustration: _By permission of the American Museum of Natural History_

Model of a three-horned Dinosaur, _Triceratops_, from Cretaceous of
Montana. Animal in life about 25 feet long]

[Illustration: _By permission of the American Museum of Natural History_

Mounting the forelegs of _Brontosaurus_, the aquatic Dinosaur]

It is not clear just what caused the race of giant reptiles to decline
and pass away. The climate did not materially change. Perhaps races grow
old, and ripe for death, after living long on the earth. It seems as if
their time was up; and the clumsy giants abdicated their reign, leaving
dominion over the sea, the air, and the land to those animals adapted to
take the places they were obliged to vacate.

THE AGE OF MAMMALS

The warm-blooded birds and mammals followed the reptiles. This does not
mean that all reptiles died, after having ruled the earth for thousands
of years. It means that changes in climate and other life conditions
were unfavourable to the giants of the cold-blooded races, and gradually
they passed away. They are represented now on the earth by lesser
reptiles, which live comfortably with the wild creatures of other
tribes, but which in no sense rule in the brute creation. They live
rather a lurking, cautious life, and have to hide from enemies, except a
few more able kinds, provided with means of defense.

There were mammals on the earth in the days of reptilian supremacy, but
they were small in size and numbers, and had to avoid any open conflict
with the giant reptiles, or be worsted in a fight. Now the time came
when the ruling power changed hands. The mammals had their turn at
ruling the lower animals. It was the beginning of things as they are
to-day, for mammals still rule. But many millions of years have probably
stood between the age when this group of animals first began to swarm
over the earth, and the time when Man came to be ruler over all created
things.

Among the reptiles of the period when the sea, the land, and the air
were swarming with these great creatures were certain kinds that had
traits of mammals. Others were bird-like. From these reptilian ancestors
birds and mammals have sprung. No one doubts this. The fossils prove it,
step by step.

Yet the rocks surprise the geologist with the suddenness with which many
new kinds of mammals appeared on the earth. Possibly the rocks
containing the bones of so many kinds were fortunately located. The
spots may have been morasses where migrating mammals were overwhelmed
while passing. Possibly conditions favored the rapid development of new
kinds, and the multiplication of their numbers. Warm, moist climate
furnished abundant succulent plant food for the herbivors, and these in
turn furnished prey for the carnivors.

The coal formed during the Tertiary Period gives added proof that the
plant life was luxuriant. The kinds of trees that grew far north of our
present warm zones have left in the rocks evidence in the form of
perfect leaves and cones and other fruits. For instance, magnolias grew
in Greenland, and palm trees in Dakota. The temperature of Greenland was
thirty degrees warmer than it is now. Our Northern States lie in a belt
that must have had a climate much like that of Florida now. Europe was
correspondingly mild.

A special chapter tells of the gradual development of the horse. One
hundred different kinds of mammals have been found in the Eocene rocks,
many of which have representative species at the same time in Europe and
America. The rocks of Asia probably have similar records.

The Eocene rocks, lowest of the Tertiary strata, contain remains of
animals the families of which are now extinct. Next overlying the
Eocene, the Miocene rocks have fossils of animals belonging to modern
families--rhinoceroses, camels, deer, dogs, cats, horses--but the genera
of which are now extinct. The Pliocene strata (above the Miocene)
contains fossils of animals so closely related to the wild animals now
on the earth as to belong to the same genera. They differ from modern
kinds only in the species, as the red squirrel is a different species
from the gray.

So the record in the rocks shows a gradual approach of the mammals to
the kinds we know, a gradual passing of the mighty forms that ruled by
size and strength, and the coming of forms with greater intelligence,
adapted to the change to a colder climate.

It sometimes happens that a farmer, digging a well on the prairie,
strikes the skeleton of a monster mammal, called the _mastodon_. This
very thing happened on a neighbour's farm when I was a girl, in Iowa.
Everybody was excited. The owner of the land dug out every bone, careful
that the whole skeleton be found. As he expected, the director of a
museum was glad to pay a high price for the bones.

[Illustration: _By permission of the American Museum of Natural History_

Restoration of an aquatic Dinosaur, _Brontosaurus excelsus_, from the
Upper Jurassic and Lower Cretaceous of Wyoming. The animal in life was
over 60 feet long]

[Illustration: _By permission of the American Museum of Natural History_

Restoration of the small carnivorous Dinosaur, _Ornitholestes hermanui_,
catching a primitive bird _Archæopteryx_. Upper Jurassic and Lower
Cretaceous]

The mastodon was about the size of an elephant, with massive limbs, and
large, heavy head that bore two stout, up-curved tusks of ivory. The
creature moved in herds like the buffalo from swamp to swamp; and old
age coming on, the individual, unable to keep up with the herd, sank to
his death in the boggy ground. The peat accumulated over his bones,
undisturbed until thousands of years elapse, and the chance digging of a
well discovers his skeleton.

Frozen in the ice of northern Siberia, near the mouths of rivers, a
number of mammoths have been found. These are creatures of the elephant
family, and belonging to the extinct race that lived in the Quaternary
Period, just succeeding the Tertiary. The ice overtook the specimens,
and they have been in cold storage ever since. For this reason, both
flesh and bones are preserved, a rare thing to happen, and rarer still
to be seen by a scientist.

The ignorant natives made a business of watching the ice masses at the
river mouth for dark spots that showed where a mammoth was encased in
the ice. If an iceberg broke off near such a place, the sun might thaw
the ice front of the glacier, until the hairy monster could at length be
reached. His long hair served for many uses, and the wool that grew
under the hair was used as a protection from the Arctic winter. The
frozen flesh was eaten; the bones carved into useful tools; but the
chief value of the find was in the great tusks of ivory, that curved
forward and pointed over the huge shoulders. It was worth a fortune to
get a pair and sell them to a buyer from St. Petersburg.

One of the finest museum specimens of the mammoth was secured by buying
the tusks of the dealer, and by his aid tracing the location of the
carcass, which was found still intact, except that dogs had eaten away
part of one foreleg, bone and all. From this carefully preserved
specimen, models have been made, exactly copying the shape and the size
of the animal, its skin, hair, and other details.

The sabre-toothed tiger, the sharp tusks of which, six to eight inches
long, made it a far more ferocious beast than any modern tiger of
tropical jungles, was a Quaternary inhabitant of Europe and America. So
was a smaller tiger, and a lion. The Irish elk, which stood eleven feet
high, with antlers that spread ten feet apart at the tips, was monarch
in the deer family, which had several different species on both
continents. Wild horses and wild cattle, one or two of great size,
roamed the woods, while rhinos and the hippopotamus kept near the
water-courses. Hyenas skulked in the shadows, and acted as scavengers
where the great beasts of prey had feasted. Sloths and cuirassed
animals, like giant armadillos, lived in America. Among bears was one,
the cave bear, larger than the grizzly. True monkeys climbed the trees.
Flamingo, parrots, and tall secretary birds followed the giant
_gastornis_, the ancestor of wading birds and ostriches, which stood ten
feet high, but had wings as small and useless as the auk of later times.

With the entrance of the modern types of trees, came other flowering
plants, and with them the insects that live on the nectar of flowers.
Through a long line of primitive forms, now extinct, flowering plants
and their insect friends conform to modern types. The record is written
in the great stone book.

The Age of Mammals in America and Europe ended with the gradual rise of
the continental areas, and a fall of temperature that ushered in the Ice
Age. With the death of tropical vegetation, the giant mammals passed
away.

THE HORSE AND HIS ANCESTORS

Every city has a horse market, where you may look over hundreds of
animals and select one of any colour, size, or kind. The least in size
and weight is the Shetland pony, which one man buys for his children to
drive or ride. Another man wants a long-legged, deep-chested hunter.
Another wants heavy draught-horses, with legs like great pillars under
them, and thick, muscular necks--horses weighing nearly a ton apiece and
able to draw the heaviest trucks. What a contrast between these slow but
powerful animals and the graceful, prancing racer with legs like
pipe-stems--fleet and agile, but not strong enough to draw a heavy load!

All these different breeds of horses have been developed since man
succeeded in capturing the wild horse and making it help him. Man
himself was still a savage, and he had to fight with wild beasts, as if
he were one of them, until he discovered that he could conquer them by
some power higher than physical strength. From this point on, human
intelligence has been the power that rules the lower animals. Its
gradual development is the story of the advance of civilization on the
earth. Through unknown thousands of years it has gone on, and it is not
yet finished.

[Illustration: _By permission of the American Museum of Natural History_

Restoration of a Siberian mammoth, _Elephas primogenius_, pursued by men
of the old stone age of Europe. Late Pleistocene epoch]

[Illustration: _By permission of the American Museum of Natural History_

Restoration of a small four-toed ancestor of the horse family, _Eohippus
venticolus_. Lower Eocene of Wyoming]

Just when and where and how our savage ancestors succeeded in taming the
wild horse of the plains and the forests of Europe or Asia is unknown.
Man first made friends with the wild sheep, which were probably more
docile than wild oxen and horses. We can imagine cold and hungry men
seeking shelter from storms in rocky hollows, where sheep were huddled.
How warm the woolly coats of these animals felt to their human
fellow-creatures crowded in with them in the dark!

It is believed that the primitive men who used stone axes as implements
and weapons, learned to use horses to aid them in their hunting, and in
their warfare with beasts and other men. Gradually these useful animals
were adapted to different uses; and at length different breeds were
evolved. Climate and food supply had much to do with the size and the
character of the breeds. In the Shetland Islands the animals are
naturally dwarfed by the cold, bleak winters, and the scant vegetation
on which they subsist. In middle Europe, where the summers are long and
the winters mild, vegetation is luxurious, and the early horses
developed large frames and heavy muscles. The Shetland pony and the
Percheron draught-horse are the two extremes of size.

What man has done in changing the types of horses is to emphasize
natural differences. The offspring of the early heavy horses became
heavier than their parents. The present draught-horse was produced,
after many generations, all of which gradually approached the type
desired. The slender racehorses, bred for speed and endurance rather
than strength, are the offspring of generations of parents that had
these qualities strongly marked. Hence came the English thoroughbred and
the American trotter.

We can read in books the history of breeds of horses. Our knowledge of
what horses were like in prehistoric times is scant. It is written in
layers of rock that are not very deep, but are uncovered only here and
there, and only now and then seen by eyes that can read the story told
by fossil skeletons of horses of the ages long past.

Geologists have unearthed from time to time skeletons of horses. It was
Professor Marsh who spent so much time in studying the wonderful beds of
fossil mammals in the western part of this country, and found among them
the skeletons of many species of horses that lived here with camels and
elephants and rhinoceroses and tigers, long before the time of man's
coming.

How can any one know that these bones belonged to a horse's skeleton?
Because some of them are like the bones of a modern horse. It is an easy
matter for a student of animal anatomy to distinguish a horse from a cow
by its bones. The teeth and the foot are enough. These are important and
distinguishing characters. It is by peculiarities in the formation of
the bones of the foot that the different species of extinct horses are
recognized by geologists.

Wild horses still exist in the wilds of Russia. Remains of the same
species have been dug out of the soil and found in caves in rocky
regions. Deeper in the earth are found the bones of horses differing
from those now living. The bones of the foot indicate a different kind
of horse--an unknown species. But in the main features, the skeleton is
distinctly horse-like.

In rocks of deeper strata the fossil bones of other horses are found.
They differ somewhat from those found in rocks nearer the surface of the
earth, and still more from those of the modern horse. The older the
rocks, the more the fossil horse differs from the modern. Could you
think of a more interesting adventure than to find the oldest rocks that
show the skeletons of horses?

The foot of a horse is a long one, though we think of it as merely the
part he walks on. A horse walks on the end of his one toe. The nail of
the toe we call the "hoof." The true heel is the hock, a sharp joint
like an elbow nearly half way up the leg. Along each side of the cannon,
the long bone of this foot, lies a splint of bone, which is the remnant
of a toe, that is gradually being obliterated from the skeleton. These
two splints in the modern horse's foot tell the last chapter of an
interesting story. The earliest American horse, the existence of which
is proved by fossil bones, tells the first chapter. The story has been
read backward by geologists. It is told by a series of skeletons, found
in successive strata of rock.

The "Bad Lands" of the arid Western States are rich in fossil remains of
horses. Below the surface soil lie the rocks of the Quaternary Period,
which included the drift laid down by the receding glaciers and the
floods that followed the melting of the ice-sheet. Under the Quaternary
lie the Tertiary rocks. These comprise three series, called the Eocene,
Miocene, and Pliocene, the Eocene being the oldest. In the middle region
of North America, ponds and marshy tracts were filled in during the
Tertiary Period, by sediment from rivers; and in these beds of clay and
other rock débris the remains of fresh-water and land animals are
preserved. Raised out of water, and exposed to erosive action of wind
and water, these deposits are easily worn away, for they have not the
solidity of older rocks. They are the crumbly Bad Lands of the West, cut
through by rivers, and strangely sculptured by wind and rain. Here the
fossil horses have been found.

_Eohippus_, the dawn horse, is the name given a skeleton found in 1880
in the lower Eocene strata in Wyoming. This specimen lay buried in a
rock formation ages older than that in which the oldest known skeleton
of this family had been found. Its discovery made a great sensation
among scientists. This little animal, the skeleton of which is no larger
than that of a fox, had four perfect toes, and a fifth splint on the
forefoot, and three toes on the hind foot. The teeth are herbivorous.

_Orohippus_, with a larger skeleton, was found in the middle Eocene
strata of Wyoming. Its feet are like those of its predecessor, except
that the splint is gone. The teeth as well as the feet are more like
those of the modern horse.

_Mesohippus_, the three-toed horse, found in the Miocene, shows the
fourth toe reduced to splints, and the skeleton as big as that of a
sheep. In this the horse family becomes fairly established.

_Hypohippus_, the three-toed forest horse, found in the middle Miocene
strata of Colorado, is a related species, but not a direct ancestor of
the modern horse.

_Neohipparion_, the three-toed desert horse, from the upper Miocene
strata, shows the three toes still present. But the Pliocene rocks
contain fossils showing gradual reduction of the two side toes,
modification of the teeth, and increase in size of the skeleton.

_Protohippus_ and _Pliohippus_, the one-toed species from the Pliocene
strata, illustrate these changes. They were about the size of small
ponies.

_Equus_, the modern horse, was represented in the Pliocene strata by a
species, now extinct, called _Equus Scotti_. This we may regard as the
true wild horse of America, for it was as large as the domesticated
horse, and much like it, though more like a zebra in some respects. No
one can tell why these animals, once abundant in this country, became
extinct at the end of the Tertiary Period. But this is undoubtedly true.

The types described form a series showing how the ancestors of the
modern horse, grazing on the marshy borders of ancient ponds, lived and
died, generation after generation, through a period covering thousands,
possibly millions, of years. Along the sides of the crumbling buttes
these ancient burying-grounds are being uncovered. Within a dozen years
several expeditions, fitted out by the American Museum of Natural
History, have searched the out-cropping strata in Dakota and Wyoming for
bones of mammals known to have lived at the time the strata were forming
in the muddy shallows along the margins of lake and marsh. Duplicate
skeletons of the primitive horse types above have been found, and vast
numbers of their scattered bones. Each summer geological excursions will
add to the wealth of fossils of this family collected in museums.

The Tertiary rocks in Europe yield the same kind of secrets. The region
of Paris overlies the estuary of an ancient river. When the strata are
laid bare by the digging of foundations for buildings, bones are found
in abundance. Cuvier was a famous French geologist who made extensive
studies of the remains of the prehistoric animals found in this old
burial-place called by scientists the Paris basin. He believed that the
dead bodies floated down-stream and accumulated in the mud of the
delta, where the tide checked the river's current.

Skeletons of the Hipparion, a graceful, three-toed horse, were found in
numbers in the strata of the Miocene time. This animal lived in Europe
while the Pliohippus and the Protohippus were flourishing in America.

A great number of species of tapir-like animals left their bones in the
Paris basin, among them a three-hoofed animal which may have been the
connecting link between the horse and the tapir families. Cuvier found
the connecting link between tapirs and cud-chewing mammals.

THE AGE OF MAN

The hairy, woolly mammoth was one of the giant mammals that withstood
the cold of the great ice flood, when the less hardy kinds were cut off
by the changing climate of the northern half of Europe and America. In
caves where the wild animals took refuge from their enemies, skeletons
of men have been found with those of the beasts. With these chance
skeletons have been found rude, chipped stone spear-heads, hammers, and
other tools. With these the savage ancestors of our race defended
themselves, and preyed on such animals as they could use for food. They
hunted the clumsy mammoth successfully, and shared the caverns in the
rocks with animals like the hyena, the sabre-toothed tiger, and the cave
bear, which made these places their homes. In California a human skull
was found in the bed of an ancient river, which was buried by a lava
flow from craters long ago extinct. With this buried skull a few
well-shaped but rough stone tools were found. This man must have lived
when the great ice flood was at its height.

In southern France, caves have been opened that contained bones and
implements of men who evidently lived by fishing and hunting. Bone
fish-hooks showed skill in carving with the sharp edges of flint
flakes. A spirited drawing of a mammoth, made on a flat, stone surface,
is a proof that savage instincts were less prominent in these cave men
than in those who fought the great reindeer and the mammoth farther
north.

In later times men of higher intelligence formed tribes, tamed the wild
horse, the ox, and the sheep, and made friends with the dog. Great heaps
of shells along the shores show where the tribes assembled at certain
times to feast on oysters and clams. Bones of animals used as food, and
tools, are found in these heaps, called "kitchen-middens." These are
especially numerous in Northern Europe. The stone implements used by
these tribes were smoothly polished. A higher intelligence expressed
itself also by the making of utensils out of clay. This pottery has been
found in shell heaps. So the rude cave man, who was scarcely less a wild
beast than the animals which competed with him for a living and a
shelter from storms and cold, was succeeded by a higher man who brought
the brutes into subjection by force of will and not by physical
strength.

The lake-dwellers, men of the Bronze Age, built houses on piles in the
lakes of Central Europe. About sixty years ago the water was low, and
these relics of a vanished race were first discovered. The lake bottoms
were scraped for further evidences of their life. Tools of polished
stone and of bronze were taken up in considerable numbers. Stored
grains and dried fruits of several kinds were found. Ornamental
trinkets, weapons of hunters and warriors, and agricultural tools tell
how the people lived. Their houses were probably built over the water as
a means of safety from attack of beasts or hostile men.

In our country the mound-builders have left the story of their manners
of life in the spacious, many-roomed tribal houses, built underground,
and left with a great variety of relics to the explorers of modern
times. These people worked the copper mines, and hammered and polished
lumps of pure metal into implements for many uses. With these are tools
of polished stone. Stores of corn were found in many mounds scattered in
the Mississippi Valley.

The cliff-dwellers of the mesas of Arizona and New Mexico had habits
like those of the mound-builders, and the Aztecs, a vanished race in the
Southwest, at whose wealth and high civilization the invading Spaniards
under Cortez marvelled. The plastered stone houses of the cliff-dwelling
Indians had many stories and rooms, each built to house a tribe, not
merely a family.

The Pueblo, the Moqui, and the Zuni Indians build similar dwellings
to-day, isolated on the tops of almost inaccessible mesas.

Millions of years have passed since life appeared on the earth.
Gradually higher forms have followed lower ones in the sea and on the
land. But not all of the lower forms have gone. All grades of plants
and animals still flourish, but the dominant class in each age is more
highly organized than the class that ruled the preceding age.

To discover the earth's treasure, and to turn it to use; to tame wild
animals and wild plants, and make them serve him; to create ever more
beautiful and more useful forms in domestication; to find out the
earth's life story, by reading the pages of the great stone book--these
are undertakings that waited for man's coming.

* * * * *

PART II

THE SKY

* * * * *

EVERY FAMILY A "STAR CLUB"

The best family hobby we have ever had is the stars. We have a star club
with no dues to pay, no officers to boss us, and only three rules:

1. We shall have nothing but "fun" in this club--no hard work. Therefore
no mathematics for us!

2. We can't afford a telescope. Therefore we must be satisfied with what
bright eyes can see.

3. No second-hand wonders for us! We want to see the things ourselves,
instead of depending on books.

You can't imagine what pleasure we have had in one short year! The baby,
of course, was too young to learn anything, and besides he was in bed
long before the stars came out. But Ruth, our seven-year-old, knows ten
of the fifteen brightest stars; and she can pick out twelve of the most
beautiful groups or constellations. We grown-ups know all of the
brightest stars, and all forty-eight of the most famous constellations.
And the whole time we have given to it would not exceed ten minutes a
day!

And the best part is the _way_ we know the stars. The sky is no longer
bewildering to us. The stars are not cold, strange, mysterious. They are
friends. We know their faces just as easily as you know your playmates.
For instance, we know Sirius, because he is the brightest. We know
Castor and Pollux, because they are twins. We know Regulus, because he
is in the handle of the Sickle. And some we know by their colours. They
are just as different as President Taft, "Ty" Cobb, Horace Fletcher and
Maude Adams. And quite as interesting!

What's more, none of us can ever get lost again. No matter what strange
woods or city we go to, we never get "turned around." Or if we do, we
quickly find the right way by means of the sun or the stars.

Then, too, our star club gives us all a little exercise when we need it
most. Winter is the time when we all work hardest and have the fewest
outdoor games. Winter is also the best time for young children to enjoy
the stars, because it gets dark earlier in winter--by five o'clock, or
long before children go to bed. It is pleasant to go out doors for half
an hour before supper and learn one new star or constellation.

Again, it is always entertaining because every night you find the old
friends in new places. No two nights are just the same. The changes of
the moon make a great difference. Some nights you enjoy the moonlight;
other nights you wish there were no moon, because it keeps you from
spying out some new star. We have a little magazine that tells us all
the news of the stars and the planets and the comets _before_ the things
happen! We pay a dollar a year for it. It is called the _Monthly
Evening Sky Map_.

When we first became enthusiastic about stars, the father of our family
said: "Well, I think our Star Club will last about two years. I judge it
will cost us about two dollars and we shall get about twenty dollars
worth of fun out of it." But in all three respects father was mistaken.

Part of the two dollars father spoke of went for a book called "The
Friendly Stars," and seventy-five cents we spent for the most
entertaining thing our family ever bought--a planisphere. This is a
device which enables us to tell just where any star is, at any time, day
or night, the whole year. It has a disc which revolves. All we have to
do is to move it until the month and the day come right opposite the
very hour we are looking at it, and then we can tell in a moment which
stars can be seen at that time. Then we go down the street where there
is a good electric light at the corner and we hold our planisphere up,
almost straight overhead. The light shines through, so that we can read
it, and it is just as if we had a map of the heavens. We can pick out
all the interesting constellations and name them just as easily as we
could find the Great Lakes or Rocky Mountains in our geography.

We became so eager not to miss any good thing that father got another
book. Every birthday in our family brought a new star book, until now we
have about a dozen--all of them interesting and not one of them having
mathematics that children cannot understand. So I think we have spent on
stars fifteen dollars more than we needed to spend (but I'm glad we did
it), and I think we have had about two hundred dollars worth of fun!
Yes, when I think what young people spend on ball games, fishing,
tennis, skating, and all the other things that children love, I am sure
our family has had about two hundred dollars worth of fun out of stars.
And there is more to come!

You would laugh to know why I enjoy stars so much. I have always studied
birds and flowers and trees and rocks and shells so much that I was
afraid to get interested in stars. I thought it wouldn't rest me. But
it's a totally different kind of science from any I ever studied! There
are no families, genera, and species among the stars, thank Heaven!
That's one reason they refresh me. Another is that no one can press them
and put them in a herbarium, or shoot them and put them in a museum. And
another thing about them that brings balm to my spirit is that no human
being can destroy their beauty. No one can "sub-divide" Capella and fill
it with tenements. No one can use Vega for a bill-board. Ah, well! we
must not be disturbed if every member of our family has a different
point of view toward the stars; we can all enjoy and love them in our
own ways.

How would you like to start a Star Club like ours? You ought to be able
to persuade your family to form one, because it need not cost a cent.
Perhaps this book will interest them all, but the better way is for you
to read about one constellation and then go out with some of the family
and find it. This book does not tell about wonderful things you can
never see; it tells about the wonderful things all of us can see.

I wish you success with your Star Club. Perhaps your uncles and aunts
will start clubs, too. We have three Star Clubs in our family--one in
New York, one in Michigan, and one in Colorado. Last winter the
"Colorado Star Gazers" sent this challenge to the "New Jersey
Night-Owls:" "_We bet you can't see Venus by daylight!_"

That seemed possible, because during that week the "evening star" was by
far the brightest object in the sky. But father and daughter searched
the sky before sunset in vain, and finally we had to ask the "Moonstruck
Michiganders" how to see Venus while the sun was shining. Back came
these directions on a postal-card: "Wait until it is dark and any one
can see Venus. Then find some tree, or other object, which is in line
with Venus and over which you can just see her. Put a stake where you
stand. Next day go there half an hour before sunset, and stand a little
to the west. You will see Venus as big as life. The next afternoon you
can find her by four o'clock. And if you keep on you will see her day
before yesterday!"

That was a great "stunt." We did it; and there are dozens like it you
can do. And that reminds me that father was mistaken about our interest
lasting only two years. We know that it will not die till we do. For,
even if we never get a telescope, there will always be new things to
see. Our club has still to catch Algol, the "demon's eye," which goes
out and gleams forth every three days, because it is obscured by some
dark planet we can never see. And we have never yet seen Mira the
wonderful, which for some mysterious reason dies down to ninth magnitude
and then blazes up to second magnitude every eleventh month.

Ah, yes, the wonders and the beauties of astronomy ever deepen and
widen. Better make friends with the stars now. For when you are old
there are no friends like old friends.

THE DIPPERS AND THE POLE STAR

I never heard of any boy or girl who didn't know the Big Dipper. But
there is one very pleasant thing about the Dipper which children never
seem to know. With the aid of these seven magnificent stars you can find
all the other interesting stars and constellations. So true is this that
a book has been written called "The Stars through a Dipper."

To illustrate, do you know the _Pointers_? I mean the two stars on the
front side of the Dipper. They point almost directly toward the Pole
star, or North star, the correct name of which is Polaris. Most children
can see the Pole star at once because it is the only bright star in that
part of the heavens.

But if you can't be sure you see the right one, a funny thing happens.
Your friend will try to show you by pointing, but even if you look
straight along his arm you can't always be sure. And then, if he tries
to tell you how far one star is from another, he will try to show you by
holding his arms apart. But that fails also. And so, we all soon learn
the easiest and surest way to point out stars and measure distances.

The easiest way to tell any one how to find a star is to get three
stars in a straight line, or else at right angles.

The surest way to tell any one how far one star is from another is by
"degrees." You know what degrees are, because every circle is divided
into 360 of them. And if you will think a moment, you will understand
why we can see only half the sky at any one time, or 180 degrees,
because the other half of the sky is on the other side of the earth.
Therefore, if you draw a straight line from one horizon, clear up to the
top of the sky and down to the opposite horizon, it is 180 degrees long.
And, of course, it is only half that distance, or 90 degrees, from
horizon to zenith. (Horizon is the point where earth and sky seem to
meet, and zenith is the point straight over your head.)

Now ninety degrees is a mighty big distance in the sky. The Pole star is
nothing like ninety degrees from the Dipper. It is only twenty-five
degrees, or about five times the distance between the Pointers. And now
comes the only thing I will ask you to remember. Look well at the two
Pointers, because the distance between them, five degrees, is the most
convenient "foot rule" for the sky that you will ever find. Most of the
stars you will want to talk about are from two to five times that
distance from some other star that you and your friends are sure of.
Perhaps this is a little hard to understand. If so, read it over several
times, or get some one to explain it to you, for when you grasp it, it
will unlock almost as many pleasures as a key to the store you like the
best.

Now, let's try our new-found ruler. Let us see if it will help us find
the eighth star in the Dipper. That's a famous test of sharp eyes. I
don't want to spoil your pleasure by telling you too soon where it is.
Perhaps you would rather see how sharp your eyes are before reading any
further. But if you can't find the eighth star, I will tell you where to
look.

Look at the second star in the Dipper, counting from the end of the
handle. That is a famous star called Mizar. Now look all around Mizar,
and then, if you can't see a little one near it, try to measure off one
degree. To do this, look at the Pointers and try to measure off about a
fifth of the distance between them. Then look about one degree (or less)
from Mizar, and I am sure you will see the little beauty--its name is
Alcor, which means "the cavalier" or companion. The two are sometimes
called "_the horse and rider_"; another name for Alcor is Saidak, which
means "the test." I shall be very much disappointed if you cannot see
Saidak, because it is not considered a hard test nowadays for sharp
eyes.

Aren't these interesting names? Mizar, Alcor, Saidak. They sound so
Arabian, and remind one of the "Arabian Nights." At first, some of them
will seem hard, but you will come to love these old names. I dare say
many of these star names are 4,000 years old. Shepherds and sailors
were the first astronomers. The sailors had to steer by the stars, and
the shepherds could lie on the ground and enjoy them without having to
twist their necks. They saw and named Alcor, thousands of years before
telescopes were invented, and long before there were any books to help
them. They saw the demon star, too, which I have never seen. It needs
patience to see those things; sharp eyes are nothing to be proud of,
because they are given to us. But patience is something to be eager
about, because it costs us a lot of trouble to get it.

Let's try for it. We've had a test of sight. Now let's have a test of
patience. It takes more patience than sharpness of sight to trace the
outline of the Little Dipper. It has seven stars, too, and the Pole star
is in the end of the handle. Do you see two rather bright stars about
twenty-five degrees from the Pole? I hope so, for they are the only
brightish stars anywhere near Polaris. Well, those two stars are in the
outer rim of the Little Dipper. Now, I think you can trace it all; but
to make sure you see the real thing, I will tell you the last secret.
The handle of the Big Dipper is bent _back_; the handle of the Little
Dipper is bent _in_.

Now, if you have done all this faithfully, you have worked hard enough,
and I will reward you with a story. Once upon a time there was a
princess named Callisto, and the great god Jupiter fell in love with
her. Naturally, Jupiter's wife, Juno, wasn't pleased, so she changed the
princess into a bear. But before this happened, Callisto became the
mother of a little boy named Arcas, who grew up to be a mighty hunter.
One day he saw a bear and he was going to kill it, not knowing that the
bear was really his own mother. Luckily Jupiter interfered and saved
their lives. He changed Arcas into a bear and put both bears into the
sky. Callisto is the Big Bear, and Arcas is the Little Bear. But Juno
was angry at that, and so she went to the wife of the Ocean and said,
"Please, never let these bears come to your home." So the wife of the
Ocean said, "I will never let them sink beneath the waves." And that is
why the Big and the Little Dipper never set. They always whirl around
the Pole star. And that is why you can always see them, though some
nights you would have to sit up very late.

Is that a true story? No. But, I can tell you a true one that is even
more wonderful. Once upon a time, before the bear story was invented and
before people had tin dippers, they used to think of the Little Dipper
as a little dog. And so they gave a funny name to the Pole star. They
called it Cynosura, which means "the dog's tail." We sometimes say of a
great man, "he was the cynosure of all eyes," meaning that everybody
looked at him. But the original cynosure was and is the Pole star,
because all the stars in the sky seem to revolve around it. The two
Dippers chase round it once every twenty-four hours, as you can convince
yourself some night when you stay up late. So that's all for to-night.

What! You want another true story? Well, just one more. Once upon a time
the Big Dipper was a perfect cross. That was about 50,000 years ago.
Fifty thousand years from now the Big Dipper will look like a steamer
chair. How do I know that? Because, the two stars at opposite ends of
the Dipper are going in a direction different from the other five stars.
How do I know that? Why, I don't know it. I just believe it. There are
lots of things I don't know, and I'm not afraid to say so. I hope you
will learn how to say "I don't know." It's infinitely better than
guessing; it saves trouble, and people like you better, because they see
you are honest. I don't know how the stars in the Big Dipper are moving,
but the men who look through telescopes and study mathematics say the
end stars do move in a direction opposite to the others, and they say
the Dipper _must_ have looked like a cross, and will look like a dipper
long, long after we are dead. And I believe them.

CONSTELLATIONS YOU CAN ALWAYS SEE

There are forty-eight well known constellations, but of these only about
a dozen are easy to know. I think a dozen is quite enough for children
to learn. And therefore, I shall tell you how to find only the showiest
and most interesting.

The best way to begin is to describe the ones that you can see almost
every night in the year, because you may want to begin any month in the
year, and you might be discouraged if I talked about things nobody could
see in that month. There are five constellations you can nearly always
see, and these are all near the Pole star.

Doubtless you think you know two of them already--the Big and the Little
Dipper. Ah, I forgot to tell you that these dippers are not the real
thing. They are merely parts of bigger constellations and their real
names are Great Bear and Little Bear. The oldest names are the right
ones. Thousands of years ago, when the Greeks named these groups of
stars, they thought they looked like two bears. I can't see the
resemblance.

But for that matter all the figures in the sky are disappointing. The
people who named the constellations called them lions, and fishes, and
horses, and hunters, and they thought they could see a dolphin, a
snake, a dragon, a crow, a crab, a bull, a ram, a swan, and other
things. But nowadays we cannot see those creatures. We can see the stars
plainly enough, and they do make groups, but they do not look like
animals. I was greatly disappointed when I was told this; but I soon got
over it, because new wonders are always coming on. I think the only
honest thing to do is to tell you right at the start that you cannot see
these creatures very well. You will spoil your pleasure unless you take
these resemblances good-naturedly and with a light heart. And you will
also spoil your pleasure if you scold the ancients for naming the
constellations badly. Nobody in the world would change those old names
now. There is too much pleasure in them. Besides, I doubt if we could do
much better. I believe those old folks were better observers than we.
And I believe they had a lighter fancy.

Let us, too, be fanciful for once. I have asked my friend, Mrs. Thomas,
to draw her notion of some of these famous creatures of the sky. You can
draw your idea of them too, and it is pleasant to compare drawings with
friends. There is only one way to see anything like a Great Bear. You
have to imagine the Dipper upside down and make the handle of the Dipper
serve for the Bear's tail. What a funny bear to drag a long tail on the
ground! Miss Martin says he looks more like a chubby hobby-horse. You
will have to make the bowl of the Dipper into hind legs and use all the
other stars, somehow, to make a big, clumsy, four-legged animal. And
what a monster he is! He measures twenty-five degrees from the tip of
his nose to the root of his tail. Yes, all those miscellaneous faint
stars you see near the Big Dipper belong to the Great Bear.

[Illustration: Orion fighting the Bull. Above are Orion's two dogs]

[Illustration: The Little Bear, the Queen in her chair, the Twins and
the Archer]

How the Great Bear looked to the people who named it thousands of years
ago, we probably shall never know. They left no books or drawings, so
far as I know. But in every dictionary and book on astronomy you can
find these bears and other animals drawn so carefully and beautifully
that it seems as if they _must_ be in the sky, and we must be too dull
to see them. It is not so. Look at the pictures in this book and, you
will see that the stars do not outline the animals. Many of them come at
the wrong places. And so it is with all the costly books and charts and
planispheres. It is all very interesting, but it isn't true. It's just
fancy. And when you once understand that it isn't true, you will begin
to enjoy the fancy. Many a smile you will have, and sometimes a good
laugh. For instance, the English children call the Dipper "Charles's
wain" or "the wagon." And the Romans called it "the plough." They
thought of those seven stars as oxen drawing a plough.

Well, that's enough about the two Bears. I want to tell you about the
other three constellations you can nearly always see. These are the
Chair, the Charioteer, and Perseus (pronounced _per'soos_).

The Chair is the easiest to find, because it is like a very bad W, and
it is always directly opposite the big Dipper, with the Pole star half
way between the two constellations. There are five stars in the W, and
to make the W into a Chair you must add a fainter star which helps to
make the square bottom of the chair. But what a crazy piece of
furniture! I have seen several ways of drawing it, but none of them
makes a comfortable chair. I should either fall over backward, or else
the back of the chair would prod me in the small of my back. The correct
name of this constellation is Cassiopeia's Chair.

I think this is enough to see and enjoy in one night. To-morrow night
let us look for the Charioteer.

I love the Charioteer for several reasons. One is that it makes a
beautiful pentagon, or five-sided figure, with its five brightest stars.
Another is that it contains the second-brightest star in the northern
part of the heavens, Capella. The only star in the north that is
brighter is Vega, but Vega is bluish white or creamy.

If you haven't already found the five-sided figure, I will tell you how
to find Capella. Suppose you had a gun that would shoot anything as far
as you wish. Shoot a white string right through the Pointers and hit the
Pole star. Then place your gun at the Pole star and turn it till it is
at right angles to that string you shot. Aim away from the big Dipper,
shoot a bullet forty-five degrees and it will hit Capella.

If that plan doesn't work, try this. Start with the star that is at the
bottom of the Dipper and nearest the handle. Draw a line half-way
between the two Pointers and keep on till you come to the first bright
star. This is Capella, and the distance is about fifty degrees.

Capella means "a kid," or "little goat," and that reminds me of the
third reason why I enjoy so much the constellation of which Capella is
the brightest star. In the old times they sometimes called this
five-sided figure "the goat-carrier." And the shepherds thought they
could see a man carrying a little goat in his left hand. I am sure you
can see the kid they meant. It is a triangle of faint stars which you
see near Capella. That's enough for to-night.

To-morrow night let us look for Perseus. I dare say you know that old
tale about Perseus rescuing the princess who was chained upon a rock.
(He cut off the snaky head of Medusa and showed it to the dragon that
was going to devour the princess, and it turned the monster to stone.
Remember?) Well, there are constellations named after all the people in
that story, but although they contain many showy stars, I could never
make them look like a hero, a princess, a king, and a queen. I do not
even try to trace out all of Perseus. For I am satisfied to enjoy a very
beautiful part of it which is called the "Arc of Perseus."

An arc, you know, is a portion of a circle. And the way to find this arc
is to draw a curve from Capella to Cassiopeia. On nights that are not
very clear I can see about seven stars in this Arc of Perseus. And the
reason I love it so much is that it is the most beautiful thing, when
seen through an opera-glass, that I know. You could never imagine that a
mere opera-glass would make such a difference. The moment I put it to my
eyes about a dozen more stars suddenly leap into my sight in and near
the Arc of Perseus. That's enough. No more stories to-night.

WINTER CONSTELLATIONS

By winter constellations I mean those you can see in winter at the
pleasantest time--the early evening. And I want you to begin with the
Northern Cross. I hope you can see this before Christmas, for, after
that, it may be hidden by trees or buildings in the west and you may not
see it again for a long while. This is because the stars seem to rise in
the east and set in the west. To prove this, choose some brilliant star
you can see at five or six o'clock; get it in line with some bush or
other object over which you can just see it. Put a stake where you
stand, and then go to the same spot about eight o'clock or just before
you go to bed. You can tell at once how much the star seems to have
moved westward.

Another thing, every star rises four minutes later every night, and
therefore the sky looks a little different at the same hour every
evening. The stars in the north set for a short time only, but when
those toward the south set they are gone a long time. For instance, the
brightest star of all is Sirius, the Dog Star, which really belongs to
the southern hemisphere. There are only about three months in the year
when children who go to bed by seven o'clock can see it--January,
February, and March.

So now you understand why I am so eager that you should not miss the
pleasure of seeing the famous Northern Cross. But although it is a big
cross, and easy to find, after you know it, I have never yet known a boy
who could show it to another boy simply by pointing at it. The surest
and best way to find it is learn three bright stars first--Altair, Vega,
and Deneb.

Altair is the brightest star in the Milky Way. It is just at the edge of
the Milky Way, and you are to look for three stars in a straight line,
with the middle one brightest. Those three stars make the constellation
called "the Eagle." The body of the eagle is Altair, and the other two
stars are the wings. I should say that Altair is about five degrees from
each of his companions. It is worth half an hour's patient search to
find the Eagle. Now these three stars in the Eagle point straight toward
the brightest star in the northern part of the sky--Vega.

To make sure of it, notice four fainter stars near it which make a
parallelogram--a sort of diamond. These stars are all part of a
constellation called "the Lyre." If you try to trace out the old musical
instrument, you will be disappointed; but here is a game worth while.
Can you see a small triangle made by three stars, of which Vega is one?
Well, one of those stars is double, and with an opera-glass you can see
which it is. On very clear nights some people with very sharp eyes can
see them lying close together, but I never could.

At last we are ready to find the celebrated Northern Cross. First draw a
line from Altair to Vega. Then draw a line at right angles to this,
until you come to another bright star--Deneb--which is about as far from
Vega as Vega is from Altair. Now this beautiful star, Deneb, is the top
of the Northern Cross. I can't tell you whether the Cross will be right
or wrong side up when you see it, or on its side. For every
constellation is likely to change its position during the night, as you
know from watching the Dipper. But you can tell the Cross by these
things. There are six stars in it. It is like a kite made of two sticks.
There are three stars in the crosspiece and four in the long piece.
Deneb, the brightest star in the cross, is at the top of the long stick.

But you mustn't expect to see a perfect cross. There is one star that is
a little out of place, and sometimes my fingers fairly "itch to put it
where it belongs." It is the one that ought to be where the long stick
of your kite is tacked to the crosspiece. And one of the stars is
provokingly faint, but you can see it. Counting straight down the long
piece, it is the third one from Deneb that is faint. It is where it
ought to be, but I should like to make it brighter. Have you the Cross
now? If not, have patience. You can't be a "true sport" unless you are
patient. You can't be a great ball-player, or hunter, or any thing else,
without resisting, every day, that sudden impulse to "quit the game"
when you lose. Be a "good loser," smile and try again. That is better
than to give up, or to win by cheating or sharp practice.

This is the last thing I want you to see in the northern part of the
sky; and if you have done a good job, let us celebrate by having a
story.

Once upon a time a cross didn't mean so much to the world as it does
now. That was before Christ was born. In those old times people did not
think of the Northern Cross as a cross. They thought of it as a Swan,
and you can see the Swan if you turn the Cross upside down. Deneb will
then be in the tail of the Swan, and the two stars which used to be at
the tips of the crosspiece now become the wings. Is that a true story?
Yes. If we lived in Arabia the children there could tell us what Deneb
means. It means "the tail."

Another story? Well, do you see the star in the beak of the Swan, or
foot of the Cross? What color is it? White? Well, they say this white
star is really made up of two stars--one yellow and the other blue. That
is one reason I want to buy a telescope when I can afford it, for even
the smallest telescope will show that. And Mr. Serviss says that even a
strong field-glass will help any one see this wonder.

I can't tell you about all the winter constellations in one chapter. We
have made friends of the northern ones. Now let's see the famous
southern ones. And let's start a new chapter.

ORION, HIS DOGS, AND THE BULL

The most gorgeous constellation in the whole sky is Orion. I really pity
any one who does not know it, because it has more bright stars in it
than any other group. Besides, it doesn't take much imagination to see
this mighty hunter fighting the great Bull. I dare say half the people
in the United States know Orion and can tell him as quick as they see
him by the famous "belt of Orion."

This belt is made of three stars, each of which is just one degree from
the next. That is why the English people call these three stars "the ell
and yard." Another name for them is "the three kings." You can see the
"sword of Orion" hanging down from his belt.

As soon as you see these things you will see the four bright stars that
outline the figure of the great hunter, but only two of them are of the
first magnitude. The red one has a hard name--Betelgeuse (pronounced
_bet-el-guz´_). That is a Frenchified word from the Arabic, meaning
"armpit," because this star marks the right shoulder of Orion. The other
first-magnitude star is the big white one in the left foot. Its name is
Rigel (pronounced _re´-jel_) from an Arabian word meaning "the foot."

You can see the giant now, I am sure. Over his left arm hangs a lion's
skin which he holds out to shield him from the bull's horns. See the
shield--about four rather faint stars in a pretty good curve? Now look
for his club which he holds up with his right hand so as to smite the
bull. See the arm and the club--about seven stars in a rather poor
curve--beyond the red star Betelgeuse? Now you have him, and isn't he a
wonder!

It is even easier to see the Bull which is trying to gore Orion. Look
where Orion is threatening to strike, and you will see a V. How many
stars in that V? Five. And which is the brightest? That red one at the
top of the left branch of the V? Yes. That V is the face of the Bull and
that red star is the baleful eye of the angry Bull which is lowering his
head and trying to toss Orion. The name of that red eye is Aldebaran
(pronounced _al-deb´-ar-an_).

I wish Aldebaran meant "red eye," but it doesn't. It is an old Arabian
word meaning the "hindmost," or the "follower," because every evening it
comes into view about an hour after you can see the famous group of
stars called the Pleiades, which are in the shoulder of the Bull.

I do not care to trace the outline of this enormous bull, but his horns
are a great deal longer than you think at first. If you will extend the
two arms of that V a long way you will see two stars which may be called
the tips of his horns. One of these stars really belongs in another
constellation--our old friend the Charioteer, the one including
Capella. Wow! what a pair of horns!

But now we come to the daintiest of all constellations--the Seven
Sisters, or Pleiades (pronounced _plee´-a-deez_).

I can see only six of them, and there is a famous old tale about the
"lost Pleiad." But I needn't describe them. Every child finds them by
instinct. Some compare them to a swarm of bees; some to a rosette of
diamonds; some to dewdrops. But I would not compare them to a dipper as
some do, because the real Little Dipper is very different. The light
that seems to drip from the Pleiades is quivering, misty, romantic,
magical. No wonder many children love the Pleiades best of all the
constellations. No wonder the poets have praised them for thousands of
years. The oldest piece of poetry about them that I know of was written
about 1,500 years before Christ. You can find it in the book of Job. But
the most poetic description of the Pleiades that I have ever read is in
Tennyson's poem "Locksley Hall," in which he says they "glitter like a
swarm of fireflies tangled in a silver braid."

There are a great many old tales about the lost Pleiad. One is that she
veiled her face because the ancient city of Troy was burned. Another
story says she ceased to be a goddess when she married a man and became
mortal. Some people think she was struck by lightning. Others believe
the big star, Canopus, came by and ran away with her. Still others
declare she was a new star that appeared suddenly once upon a time, and
after a while faded away.

For myself, I do not believe any of these stories. One reason why I
don't is that a seventh star is really there, and many people can really
see it. Indeed, there are some people so sharp-eyed that on clear nights
they can see anywhere from eight to eleven. And, what is more, they can
draw a map or chart showing just where each star seems to them to be.

But the most wonderful stories about the Pleiades are the true stories.
One is that there are really more than 3,000 stars among the Pleiades.
Some of them can be seen only with the biggest telescopes. Others are
revealed only by the spectroscope. And some can be found only by means
of photography.

But the most amazing thing about the Pleiades is the distances between
them. They look so close together that you would probably say "the moon
seems bigger than all of them put together." Sometimes the moon comes
near the Pleiades, and you expect that the moon will blot them all out.
But the astronomers say the full moon sails through the Pleiades and
covers only one of them at a time, as a rule. They even say it is
possible for the moon to pass through the Pleiades without touching one
of them! I should like to see that. If anything like it is going to
occur, the magazine I spoke of in the first chapter will tell me about
it. And you'd better believe I will stay up to see that, if it takes all
night!

There are two more constellations in the southern part of the sky that
ought to be interesting, because they are the two hunting dogs that help
Orion fight the Bull. But I can't trace these animals, and I don't
believe it is worth while. The brightest stars in them everybody can see
and admire--Sirius, the Bigger Dog, and Procyon, the Smaller Dog.

Every one ought to know Sirius, because he is the brightest star of all.
(Of course, he is not so bright as Venus and Jupiter, but they are
planets.) To find him, draw a line from the eye of the Bull through the
belt of Orion and extend it toward the southeast about twenty degrees.
They call him the Dog star because he follows the heels of Orion. And
people still call the hottest days of summer "dog days" because 400
years before Christ the Romans noticed that the Dog star rose just
before the sun at that time. The Romans thought he chased the sun across
the sky all day and therefore was responsible for the great heat. But
that was a foolish explanation. And so is the old notion that dogs are
likely to go mad during the dog days "because the dog star is in the
ascendant." So is the idea that Sirius is an unlucky star.

There are no lucky or unlucky stars. These are all superstitions, and we
ought to be ashamed to believe any superstition. Yet for thousands of
years before we had public schools and learned to know better, people
believed that every one was born under a lucky star or an unlucky one,
and they believe that farmers ought to plant or not plant, according to
the size of the moon. Now we know that is all bosh. Those old
superstitions have done more harm than good. One of the most harmful was
the belief in witches. Let us resolve never to be afraid of these old
tales, but laugh at them.

Why should anybody be afraid of anything so lovely as Sirius? I used to
think Sirius twinkled more than any other star. But that was bad
reasoning on my part. I might have noticed that every star twinkles more
near the horizon than toward the zenith. I might have noticed that stars
twinkle more on clear, frosty nights than when there is a little uniform
haze. And putting those two facts together I might have reasoned that
the stars never really twinkle at all; they only seem to. I might have
concluded that the twinkling is all due to the atmosphere--that blanket
of air which wraps the earth around. The nearer the earth, the thicker
the air, and the more it interferes with the light that comes to us from
the stars.

They say that Sirius never looks exactly alike on two successive nights.
"It has a hundred moods," says Mr. Serviss, "according to the state of
the atmosphere. By turns it flames, it sparkles, it glows, it blazes, it
flares, it flashes, it contracts to a point, and sometimes when the air
is still, it burns with a steady white light." (Quotation somewhat
altered and condensed.)

It is a pity that so fine a star as Procyon should be called the
"Smaller Dog," because it suffers unjustly by comparison with Sirius. If
it were in some other part of the sky we might appreciate it more,
because it is brighter than most of the fifteen first-magnitude stars we
can see. My brother William has grown to love it, but perhaps that is
because he always "sympathizes with the under dog." He was the youngest
brother and knows. And curiously enough he was nicknamed "the dog"--just
why, I don't know.

To find Procyon, drawn a line from Sirius northeast about twenty
degrees. And to make sure, draw one east from Betelgeuse about the same
distance. These three stars make a triangle of which the sides are
almost equal.

The name Procyon means "before the dog" referring to the fact that you
can see him fifteen or twenty minutes earlier every night than you can
see Sirius.

The only kind word about Procyon I have heard in recent years was in
connection with that miserable business of Dr. Cook and the North Pole.
A Captain Somebody-or-other was making observations for Dr. Cook, and he
wanted to know what time it was. He had no watch and didn't want to
disturb any one. So he looked out of the window and saw by the star
Procyon that it was eleven o'clock.

That sounds mysterious, but it is easy if you have a planisphere like
ours. Last winter when we were all enjoying Orion, the Bull, and the two
Dogs, I used to whirl the planisphere around to see where they would be
at six o'clock at night, at eight, at ten, at midnight, and even at six
o'clock in the morning. And so, if I waked up in the night I could tell
what time it was without even turning my head. Sometimes I looked out of
my window, saw Orion nearly overhead and knew it must be midnight. And
sometimes I woke up just before daybreak and saw the great Bull backing
down out of sight in the west, the mighty Hunter still brandishing his
club, and his faithful Dogs following at his heels.

SEVEN FAMOUS CONSTELLATIONS

There are only seven more constellations that seem to me interesting
enough for every one to know and love all his life. These are:

The Lion (Spring)

The Twins (Spring)

The Virgin (Summer)

The Herdsman (Summer)

The Northern Crown (Summer)

The Scorpion (Summer)

Southern Fish (Autumn)

I have named the seasons when, according to some people, these
constellations are most enjoyable. But these are not the only times when
you can see them. (If you had that seventy-five-cent planisphere, now,
you could always tell which constellations are visible and just where to
find them.) No matter what time of year you read this chapter, it is
worth while to go out and look for these marvels. You can't possibly
miss them all.

Have you ever seen a Sickle in the sky? It's a beauty, and whenever I
have seen it it has been turned very conveniently for me, because I am
left-handed. It is so easy to find that I am almost ashamed to tell. But
if you need help, draw a line through the Pointers backward, away from
the Pole star, about forty degrees, and it will come a little west of
the Sickle. The Sickle is only part of the Lion--the head and the
forequarters. Only fanciful map-makers can trace the rest of the Lion.
The bright star at the end of the handle is Regulus, which means "king,"
from the stupid old notion that this star ruled the lives of men. To
this day people speak of the "Royal Star," meaning Regulus. And at the
end of this chapter I will tell you about three other stars which the
Persians called "royal stars."

Another constellation which children particularly love is the
Twins--Castor and Pollux. But the sailors got there first! For thousands
of years the twins have been supposed to bring good luck to sailors. I
don't believe a word of it. But I do know that sailors gloat over Castor
and Pollux, and like them better than any other stars. The whole
constellation includes all the stars east of the Bull and between the
Charioteer and Procyon. But another way to outline the twins is to look
northeast of Orion where you will see two rows of stars that run nearly
parallel. To me the brothers seem to be standing, but all the old
picture-makers show them sitting with their arms around each other, the
two brightest stars being their eyes. The eyes are about five degrees
apart--the same as the Pointers.

Pollux is now brighter than Castor, but for thousands of years it was
just the other way. It is only within three hundred years that this
change has taken place. Whether Castor has faded or Pollux brightened,
or both, I do not know. Anyhow, Castor is not quite bright enough to be
a first magnitude star. Three hundred years is a short time in the
history of man, and only a speck in the history of the stars. Three
hundred years ago they killed people in Europe just because of the
church they went to. That was why the Pilgrim Fathers sailed from
England in 1620, and made the first permanent settlement in America,
except, of course, Jamestown, Va., in 1607.

There are plenty of stories about old Castor and Pollux, and, like all
the other myths, they conflict, more or less. But all agree that these
two brothers went with Jason in the ship Argo, shared his adventures and
helped him get the golden fleece. And all agree that Castor and Pollux
were "born fighters." And that is why the Roman soldiers looked up to
these stars and prayed to them to help them win their battles.

Now for the four summer constellations every one ought to know. The
first thing to look for is two famous red or reddish stars--Arcturus and
Antares.

The way you find Arcturus is amusing. Look for the Big Dipper and find
the star at the bottom of the dipper nearest the handle. Got it? Now
draw a curve that will connect it with all the stars in the handle, and
when you come to the end of the handle keep on till you come to the
first very bright star--about twenty-five degrees. That is the monstrous
star Arcturus, probably the biggest and swiftest star we can ever see
with the naked eye in the northern hemisphere. He is several times as
big as our sun, and his diameter is supposed to be several million
miles. He is called a "runaway sun," because he is rushing through space
at the rate of between two hundred and three hundred miles a second.
That means between seventeen and thirty-four million miles a day!

He is coming toward us, too! At such a rate you might think that
Arcturus would have smashed the earth to pieces long ago. But he is
still very far away, and there is no danger. Some people say that if Job
were to come to life, the sky would seem just the same to him as it did
3,400 years ago. The only difference he might notice would be in
Arcturus. That would seem to him out of place by a distance about three
times the apparent diameter of the moon.

Some people believe this because Job said, "Canst thou guide Arcturus
with his sons?" and therefore they imagine that he meant this red star.
But I believe he meant the Big Dipper. For in King James's time, when
the Bible was translated into English, the word "Arcturus" meant the Big
Dipper or rather the Great Bear. And for centuries before it meant the
Great Bear. One proof of it is that "Arcturus" comes from an old Greek
word meaning "bear"--the same word from which we get arctic. It is only
within a few hundred years that astronomers have agreed to call the
Great Bear "Ursa Major," and this red star Arcturus. So I think all the
books which say Job mentioned this red star are mistaken. I believe
Webster's Dictionary is correct in this matter, and I believe the
Revised Version translates Job's Hebrew phrase more correctly when it
says, "Canst thou guide the Bear with her train?"

Anyhow, Arcturus is a splendid star--the brightest in the constellation
called the "Herdsman" or Boötes. It is not worth while to trace the
Herdsman, but here is an interesting question. Is Arcturus really red?
The books mostly say he is yellow. They say he looks red when he is low
in the sky, and yellow when he is high. How does he look to you? More
yellow than red?

Well, there's no doubt about Antares being red. To find him, draw a long
line from Regulus through Arcturus to Antares, Arcturus being more than
half way between the other two. But if Regulus and the Sickle are not
visible, draw a line from Altair, at right angles to the Eagle, until
you come to a bright star about sixty degrees away. You can't miss
Antares, for he is the only red star in that part of the sky.

Antares belongs to a showy constellation called the Scorpion. I cannot
trace all the outline of a spider-like creature, but his poisonous tail
or "stinger" is made by a curved line of stars south and east of
Antares. And you can make a pretty fan by joining Antares to several
stars in a curve which are west of Antares and a little north. There is
an old tale that this Scorpion is the one that stung Orion to death when
he began to "show off" and boast that there was no animal in the world
that could kill him.

Another very bright star in the southern part of the sky is Spica. To
find it, start with the handle of the Dipper, and making the same
backward curve which helped you to find Arcturus, keep on till you come
to the white star Spica--say thirty degrees beyond Arcturus. This is the
brightest star in the constellation called "the Virgin." It is not worth
while trying to trace her among nearly forty faint stars in this
neighbourhood. But she is supposed to be a winged goddess who holds up
in her right hand an _ear of wheat_, and that is what Spica means.

Now for an autumn constellation--the Southern Fish. I don't care if you
fail to outline a fish, but I do want you to see the bright star that is
supposed to be in the fish's mouth. And I don't want you to balk at its
hard name--Fomalhaut (pronounced _fo´-mal-o_). It is worth a lot of
trouble to know it as a friend. To find it, you have to draw an
exceedingly long line two-thirds of the way across the whole sky. Start
with the Pointers. Draw a line through them and the Pole star and keep
clear on until you come to a solitary bright star rather low down in the
south. That is Fomalhaut. It looks lonely and is lonely, even when you
look at it through a telescope.

And now for the last story. Once upon a time the Persians thought there
must be four stars that rule the lives of men. So they picked out one in
the north and one in the south and one in the east and one in the west,
just as if they were looking for four bright stars to mark the points of
the compass. If you want to find them yourself without my help don't
read the next sentence, but shut this book and go out and see. Then
write down on a piece of paper the stars you have selected and compare
them with the list I am about to give. Here are the four royal stars of
the Persians: Fomalhaut for the north, Regulus for the south, Aldebaran
for the east, and Antares for the west.

Why doesn't this list agree with yours? Because Persia is so far south
of where we live. Ah, there are very few things that are absolutely
true. Let's remember that and not be too sure: for everything depends
upon the point of view! I hope you will see Fomalhaut before Christmas,
before he disappears in the west. He is with us only five months and is
always low--near the horizon. But the other seven months in the year he
gladdens the children of South America and the rest of the southern
hemisphere, for they see him sweeping high and lonely far up into their
sky and down again.

But the loveliest of all the constellations described in this chapter is
the Northern Crown. It is not a perfect crown--only about half a
circle--but enough to suggest a complete ring. Look for it east of
Arcturus. I can see seven or eight stars in the half-circle, one of
which is brighter than all the others. That one is called "the Pearl."
The whole constellation is only fifteen degrees long, but "fine things
come in small packages"; and children grow to love the Northern Crown
almost as much as they love the Pleiades.

THE TWENTY BRIGHTEST STARS

If you have seen everything I have described so far, you have reason to
be happy. For now you know sixteen of the most famous constellations and
fifteen of the twenty brightest stars. There are only twenty stars of
the first magnitude. "Magnitude" ought to mean size, but it doesn't. It
means brightness--or rather the apparent brightness--of the stars when
seen by us. The word magnitude was used in the old days before
telescopes, when people thought the brighter a star is the bigger it
must be. Now we know that the nearer a star is to us the brighter it is,
and the farther away the fainter. Some of the bright stars are
comparatively near us, some are very far. Deneb and Canopus are so far
away that it takes over three hundred years for their light to reach us.
What whoppers they must be--many times as big as our sun.

Here is a full list of the twenty stars of the first magnitude arranged
in the order of their brightness. You will find this table very useful.

The five stars marked * belong to the Southern hemisphere, and we can
never see them unless we travel far south. Last winter I went to Florida
and saw Canopus, but to see the Southern Cross you should cross the
Tropic of Cancer.

HOW TO LEARN MORE

All I can hope to do in this book is to get you enthusiastic about
astronomy. I don't mean "gushy." Look in the dictionary and you will
find that the enthusiast is not the faddist. He is the one who sticks to
a subject for a lifetime.

Nor do I care a rap whether you become an astronomer--or even buy a
telescope. There will be always astronomers coming on, but there are too
few people who know and love even a few of the stars. I want you to make
popular astronomy a life-long hobby. Perhaps you may have to drop it for
ten or fifteen years. Never mind, you will take up the study again. I
can't expect you to read a book on stars if you are fighting to make a
living or support a family, unless it really rests you to read about the
stars. It does rest me. When things go wrong at the office or at home, I
can generally find rest and comfort from music. And if the sky is clear,
I can look at the stars, and my cares suddenly seem small and drop away.

Let me tell you why and how you can get the very best the stars have to
teach you, without mathematics or telescope. Follow this programme and
you need never be afraid of hard work, or of exhausting the pleasures
of the subject. Go to your public library and get one of the books I
recommend in this chapter, and read whatever interests you. I don't care
whether you take up planets before comets or comets before planets, but
whatever you do do it well. Soak the interesting facts right in. Nail
them down. See everything the book talks about. Make notes of things to
watch for. Get a little blank book and write down the date you first saw
each thing of interest. Write down the names of the constellations you
love most. Before you lay down any star book you are reading, jot down
the most wonderful and inspiring thing you have read--even if you have
only time to write a single word that may recall it all to you. Treasure
that little note book as long as you live. Every year it will get more
precious to you.

Now for the books:

1. _Martin._ _The Friendly Stars._ Harper & Brothers, New York, 1907.

This book teaches you first the twenty brightest stars and then the
constellations. I cannot say that this, or any other, is the "best
book," but it has helped me most, and I suppose it is only natural that
we should love best the first book that introduces us to a delightful
subject.

2. _Serviss._ _Astronomy with the Naked Eye._ Harper & Brothers, New
York, 1908.

This teaches you the constellations first and the brightest stars
incidentally. Also it gives the old myths.

3. _Serviss._ _Astronomy with an Opera-Glass._ D. Appleton & Co., New
York, 1906.

4. _Serviss._ _Pleasures of the Telescope._ D. Appleton & Co., New York,
1905.

5. _Milham._ _How to Identify the Stars._ The Macmillan Co., New York,
1909.

This gives a list of eighty-eight constellations, including thirty-six
southern ones, and has tracings of twenty-eight.

6. _Elson._ _Star Gazer's Handbook._ Sturgis & Walton Co., New York,
1909.

About the briefest and cheapest. Has good charts and makes a specialty
of the myths.

7. _Serviss._ _Curiosities of the Sky._ Harper & Brothers, New York.

Tells about comets, asteroids, shooting stars, life on Mars, nebulæ,
temporary stars, coal-sacks, Milky Way, and other wonders.

8. _Ball._ _Starland._ Ginn & Co., Boston, New York, etc., 1899.

This tells about a great many interesting experiments in astronomy that
children can make.

* * * * *

If I had only a dollar or less to spend on astronomy I should buy a
planisphere. I got mine from Thomas Whittaker, No. 2 Bible House, New
York. It cost seventy-five cents, and will tell you where to find any
star at any time in the year. It does not show the planets, however. A
planisphere that will show the planets costs about five dollars.
However, there are only two very showy planets, viz., Venus and Jupiter.
Any almanac will tell you (for nothing) when each of these is morning
star, and when each of them is evening star.

The best newspaper about stars, as far as I know, is a magazine called
_The Monthly Evening Sky Map_, published by Leon Barritt, 150 Nassau
St., New York. It costs a dollar a year. It gives a chart every month,
showing all the planets, and all the constellations. Also it tells you
about the interesting things, like comets, before they come.

Good-bye. I hope you will never cease to learn about and love the earth
and the sky. Perhaps you think you have learned a great deal already.
But your pleasures have only begun. Wait till you learn about how the
world began, the sun and all his planets, the distances between the
stars, and the millions of blazing suns amid the Milky Way!

THE END

[Illustration: THE SKY IN WINTER]

NOTE.--These simplified star maps are not as accurate as a planisphere,
but they may be easier for children. All star maps are like ordinary
maps, except that east and west are transposed. The reason for this is
that you can hold a star map over your head, with the pole star toward
the north, and the map will then match the sky. These maps contain some
constellations that are only for grown-ups to study. The Winter
constellations every child should know are:

AURIGA, the Charioteer
CANIS MAJOR, the Big Dog
CANIS MINOR, the Little Dog
CASSIOPEIA, the Queen in Her Chair
CYGNUS, the Swan
LEO, the Lion
ORION, the Hunter
PERSEUS, Which Has the Arc
TAURUS, the Bull
URSA MAJOR, the Great Bear
URSA MINOR, the Little Bear

[Illustration: THE SKY IN SPRING]

NOTE.--Once upon a time all the educated people spoke Latin. It was the
nearest approach to a universal language. So most of the constellations
have Latin names. The English, French and German names are all
different, but if all children would learn the Latin names they could
understand one another. The Spring constellations every child should
know are:

LEO, the Lion
LYRA, the Lyre
CASSIOPEIA, the Queen in her Chair
SCORPIO, the Scorpion
URSA MAJOR, the Great Bear
URSA MINOR, the Little Bear
VIRGO, the Virgin

[Illustration: THE SKY IN SUMMER]

NOTE.--Every sky map is good for three months, in this way: If this is
correct on June 1st at 10 P.M., it will be correct July 1st at 8 P.M.,
and August 1st at 6 P.M. This is because the stars rise four minutes
earlier every night. Thus, after thirty days, any star will rise thirty
times four minutes earlier, or 120 minutes, or two hours. Children need
not learn all the Summer constellations. The most interesting are:

AURIGA, the Charioteer
CANIS MAJOR, the Big Dog
CYGNUS, the Swan
LYRA, the Lyre
SCORPIO, the Scorpion

[Illustration: THE SKY IN AUTUMN]

NOTE.--This book tells how to find all the most interesting stars and
constellations without maps, but many people prefer them. How to use
star maps is explained under "The Sky in Winter." The Autumn
constellations most interesting to children are:

AQUILA, the Eagle
AURIGA, the Charioteer
CASSIOPEIA, the Queen in Her Chair
CYGNUS, the Swan
LYRA, the Lyre
PERSEUS, Which Has the Arc
TAURUS, the Bull
URSA MAJOR, the Great Bear
URSA MINOR, the Little Bear

Transcriber's notes

Page 124 "streams, runing" corrected to "streams, running"
Page 127 "where he globe" corrected to "where the globe"
Page 138 "ceatures to prove" corrected to "creatures to prove"
Page 216 "this consellation is" corrected to "this constellation is"
Page 203 "Everybirth day" corrected to "Every birthday"

*** End of this LibraryBlog Digital Book "Earth and Sky Every Child Should Know - Easy studies of the earth and the stars for any time and place" ***

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