Book V -- Physiography
The Science of the Land and of
the Sea
Contents
The Oceans . . . . . . . . . . . . . . .185
Depth of the Sea . . . . . . . . . . .186
Soundings . . . . . . . . . . . . . . . .186
The Sea Bottom . . . . . . . . . . .187
Dredging . . . . . . . . . . . . . . . . .187
Ooze . . . . . . . . . . . . . . . . . . . . 187
Fish . . . . . . . . . . . . . . . . . . . . 188
Phosphorescent Fish . . . . . . . .188
Deep-Sea Fish . . . . . . . . . . . . .189
Icebergs . . . . . . . . . . . . . .. . . .189
Glaciers . . . . . . . . . . . . . . . . . 191
Bowlders . . . . . . . . . . . . . . . . . 191
Pack-Ice . . . . . . . . . . . . . . .. . 191
Ice-Worn Rocks . . . . . . . . . . .192
Rivers and Streams . . . . . . . . . 193
Underground Water . . . . . . . .193
Meandering Streams . . . . . . . 194
Habits of Rivers . . . . . . . . . . . 195
Canyons . . . . . . . . . . . . . . . . . 196
Flood Plains . . . . . . . . . . . . . . 197
Waterfalls . . . . . . . . . . . . . . . .198
The Land . . . . . . . . . . . . . . . . 199
Changes in the Land . . . . . . . .199
Mountains sculptured by Rains . . 200
Sand Dunes . . . . . . . . . . . . . . .200
Waste of the Land . . . . . . . . . 201
Slow Motions of the Con-
tinents . . . . . . . . . . . . . . . . 202
Fossils . . . . . . . . . . . . . . . . . . 203
Sandstones . . . . . . . . . . . . . . .204
The Interior of the Earth . . . . 205
Stratified Rocks . . . . . . . . . . 205
Formation of Mountain Ranges .. . . . .205
The Oldest Mountains in America . . . .208
The Age of the Earth . . . . . . . . . . . . .209
Age of Different Parts of America . .. 209
Age of Man on the Earth . . . . 211
Flint Weapons . . . . . . . . . . . . 211
The Earliest Drawing . . . . . . . 211
The First Plaything . . . . . . . . .212
A Geyser . . . . . . . . . . . . . . . . .213
The Internal Heat of the Earth 214
Volcanoes . . . . . . . . . . . . . . . . 214
Teneriffe . . . . . . . . . . . . . . . . . 214
Kilauea . . . . . . . . . . . . . . . . . . 215
Vesuvius . . . . . . . . . . . . . . . . . 215
Herculaneum and Pompeii . . . 215
Volcanoes in the United States 218
Old Lava Fields in Idaho, Oregon, and Washington . . .218
Earthquakes . . . . . . . . . . . . . . . . . . . . 218
Cause of Earthquakes . . . . . . . 219
The Charleston Earthquake (1886). . . . . . . . . . 219
The Mississippi Valley Earthquake (1811). . . . . 222
What to do during an Earthquake . . . . . . . . . . 222
Earthquake Detectors--how to make them . . . . 222
The Lisbon Earthquake (1755) . . . . . . . 223
Sea Waves . . . . . . . . . . . . . . . . . . . . . . 224
The United States Ship Wateree At Iquique (1868) . . . .224
Fig 162 The Grand Canyon of the Colorado River
pg 185
The Oceans.--The children were
looking at a large globe and talking about it. First they turned it so
as to show the water hemisphere, then so as to show the land
hemisphere, and then so as to show the two poles--arctic and Antarctic.
(See the pictures, Figs. 6 and 7.)
Mary. I never quite understood
before how much sea there was and how very little land.
Tom. The books say that three
quarters of the surface of the earth are water, and this globe makes
you believe it.
"You'd believe it, if you ever made a long voyage by sea," said Tom's
father. "Once I sailed straight west for a whole month in the Pacific,
from Peru to Tahiti, and at the end of the month I was only halfway
across to Australia. I knew all about maps and globes, but I never
realized how large the Pacific was until that time. I've had a respect
for the mere size of it ever since."
Tom. The Atlantic is large,
too, but we don't think of it as so very large because the streamers to
England are so very swift. They cross from New York to Liverpool in six
days.
pg 186
Jack. There's another thing.
The Atlantic has cables across it in many places and we read the
telegrams from Europe in the newspapers every day. That makes England
seem near.
Mary. How deep is the sea,
Jack?
Jack. Oh, it is of very
different depths in different places. The Atlantic Ocean, on the
average, is a little over two miles, and the Pacific is deeper--about
three miles. But you know there are places where the sea is much
deeper--nearly six miles. Near our new island of Guam in the Pacific
there is a spot 31,600 feet deep.
Fig 163 A Deep-Sea
Dredge--It is a large bag or scoop bringing up parts of the ocean
floor.
Little shells and so forth are caught by the tassels.
Fred. The highest mountains
are about five miles; the sea is as deep as the mountains are high.
That is a way to remember.
Jack. Yes; but you must
remember too, that there is very much more area of deep sea than of
mountain regions, so you could not fill up the sea by putting the
mountains in it. You would have to borrow some land from another planet
to fill it up.
Depth of the Sea.--"I suppose
they find the depth of the sea by sounding with a weight on the end of
a rope, don't they?--just as we do in a pond," said Fred.
Tom. They do not use rope;
they use piano wire; the rope would float--or at least it would not
sink as quickly as wire does.
Jack. Yes, they use miles of
fine piano wire and a heavy weight that drops off when it strikes the
bottom. That makes it easy to reel the wire in again.
pg 187
Agnes. What is at the bottom
of the sea, Jack?
Jack. Anywhere near the land
the sea bottom is covered with mud. The rivers and the rains carry the
soil of the land far out to sea and the ocean floor is covered with it.
Little pieces of the rocks of the land are carried out to sea, and you
find the same rocks in this mud that we have on the land. The
Mississippi or the Amazon river carries its mud out to sea for hundreds
of miles. When you get very far from land the dredge brings up a
different kind of rock. The little pieces of rock in the sea bottom
very far from land have sharp angles. They have not been rolled about
by surf and their corners are sharp like crystals.
Besides these rocks the dredge brings up the shells of little creatures
that live near the surface of the sea. When they die their shells sink
to the bottom, and there are millions and millions of them, so that a
good part of the ocean floor is covered with a kind of ooze--they call
it--mostly made of these shells. Then we find the bones of fishes, the
teeth
Fig 164 A bit of ocean
floor from a region
within a few hundred miles of the land.
Notice that the fragments of rock are rounded,
which shows that they have been washed by waves.
Fig 165 A bit of the red clay of the floor of the deep
ocean far from shore.
Notice that the fragments of the rock have sharp angles,
which proves that they have not been rolled about by surf
and do not come from the washings of the continents.
pg 188
of sharks, and things of that kind imbedded in the clay; and small
pieces of ivory, too, with pieces of meteors which have fallen into the
sea. You see the ocean floor is made up of at least three different
things--the washings of the continents, the red clay, and the ooze of
shells and the like.
Tom. Then, of course, the
ocean is full of fish.
Jack. There are plenty of fish
near the surface. They live where their food is, and most of it is near
the surface. There are some fish in the greatest depths, too, but the
living things there are mostly crabs, starfish, shellfish, and so
forth. You know the surface of the water is crowded with jellyfish of
all kinds.
The jellyfish are phosphorescent. They glow when they are disturbed
just as a sulphur match glows when you rub it with your fingers in the
dark. All the light at the bottom of the sea comes from jellyfish. The
sunlight does not go very deep down.
Tom. How do you know there is
any light at the bottom of the sea, then?
Jack. Because the deep-sea
fish have eyes. If there were no light whatever, all the fish would, in
time, lose their eyes, just as the fish in the Mammoth Cave have; but
many of the deep-sea fish have eyes.
Fig 166 A floating jellyfish
pg 189
Fred. There are fish--whales
and so forth--near the surface of the sea; and there are starfish and
crabs and shellfish at the bottom. What is in between?
Fig 167 A deep-sea
fish with eyes
Fig 168 A deep-sea
spirula, a king of cuttlefish.
The real fish is just twice the size of the picture.
Jack. Almost nothing, Fred;
just dark, quiet, cold water, with no seaweed, no plants, no animals,
and no fish. There is no life there to speak of; no light and no
motion, for the waves that we see on the surface do not go down very
deep either. The middle depths of the ocean are the most dreary and the
most monotonous places you can conceive of. The arctic regions are gay
compared to them!
Icebergs.--"How do you children
suppose an iceberg is formed?" said Jack.
Mary. I suppose the sea water
freezes and makes it.
Fred. That will not do, Mary.
Don't you see that water could not freeze high up in the air like that?
Jack. Do any of you know?
Tom. Icebergs break off from
the ends of glaciers, they say.
pg 190
Fig 169 A floating
iceberg--Ice is a little lighter than water, and it floats therefore.
About one-seventh of an iceberg shows above the surface; six sevenths
are below.
Fig 170 Icebergs breaking off from the end of Muir
Glacier in Alaska
pg 191
Glaciers.--"And glaciers are
rivers of ice flowing slowly down from the mountains," said Jack.
Agnes. Do they flow like
rivers?
Jack. They flow somewhat as
rivers do; yes, only very much slower--a few hundred feet a year, for
instance; but they often keep on till they reach the sea (see Fig.
170), and there huge pieces break off and form bergs.
Fig 171 A bowlder of
rock that was once on the top of a glacier--The glacier brought it from
far away, and the rock was left here when the glacier melted.
Tom. Then the water of
icebergs is not salt; it is fresh.
Jack. Yes, it is rain water
that has fallen as snow, you see.
Mary. But the sea water does
freeze, Jack, doesn't it?
Jack. Certainly; and makes the
great ice fields that you have read about.
Some of these fields are very thick, especially when they have been
packed together by tides and currents. When the ice first freezes it is
smooth, of course, but after it has been packed it is horribly rough.
It is often entirely too rough to travel over, and that is the reason
why it is so hard to get to the north pole.
Tom. You go as far as you can
in your ship, and then you take dog sledges, and finally you come to
ice too rough to travel over. Is that it?
Jack. Yes; the ice blocks are
as big as houses and are all piled together every which way, and a
day's journey is often only three or four miles.
pg 192
Fig 172 A rock on the
coast of Maine that was once under a glacier and has been worn smooth
by the ice.
Fig 173 The beginning of a glacier high up in the mountains.
The snow of the peaks slides into and down the valleys and
becomes ice by the pressure of the tightly packed mass.
If you pack a snowball very tight, it becomes nearly pure ice.
pg 193
Rivers and Streams.--"Did you
children ever think of how a drop of rain water gets from the mountains
into the sea?" said Jack. "It is worth while. Suppose you begin by
thinking of what happens when the rain falls on a plowed field. The
next time there is a rain you must look carefully and see exactly what
takes place."
Fig 174 A ship frozen
in an ice field
Underground Water.--"Part of
the water soaks into the ground, but most of it urns off in little
streams," said Tom.
Jack. What becomes of the
water that soaks into the ground, Agnes?
Agnes. Why, a good deal of it
stays there. If you dig down, the ground is always moist.
Jack. And when corn is planted
in the field it gets a good part of its water from the earth. You know
there is a great deal of water in Indian corn--in the ears and in the
stalks; so some of last month's rain will be in the sweet corn you will
eat
pg 194
next August. Now, what becomes of the water that does not get into the
ground but runs off?
Fred. Some of it gets into the
air as moisture and makes fog and clouds.
Agnes. Yes, and those clouds
may bring rain again.
Mary. But not on our field;
they will be far away the next time it rains.
Fred. And most of the water
runs off in little streams and by and by gets into the brook.
Mary. And the brook carries it
off to the river, and the river to another river, and so on, till it
gets to the sea.
Fig 175 Little
streamlets of rain water running off plowed ground.
Jack. Does the water ever flow
uphill?
Agnes. No, of course not.
Jack. Then it is downhill all
the way from our field to the sea. If you followed a drop of water in
the brook, it would always be traveling downhill, but it would not go
straight.
Fred. I should think not! No
rivers are straight.
Jack. A river in Asia Minor,
called the Maeander, was so full of bends that it gave a name to that
habit of rivers; we call them meandering rivers, and the bends meanders.
pg 195
Agnes. Can you say that rivers
have habits, Jack?
Jack. Why certainly, Agnes; a
habit is a custom, that is all.
It is a habit of rivers to flow downhill, to be crooked, to carry
little particles of sand and soil in their streams, to roll pebbles and
stones along their beds, and so on; it is a habit of rivers to
work--they are industrious.
Fig 176 A meandering
brook
Agnes. Oh, Jack--industrious!
Tom. Well, they are. They
carry no end of soil and rocks along in their course, and they work day
and night, too.
Jack. You might almost think a
river was alive if you counted up all the different things it did, and
you might almost say a river had a purpose in life, just as a man has.
pg 196
Take the Colorado River, for instance; its purpose is to get to the sea
in the best way possible, and it has industriously cut a way through
rocks till its canyon is nearly a mile deep. (See the picture on page
184.) Some rivers actually steal.
Agnes. Oh, Jack! What do they
steal?
Jack. Well, for one thing,
they steal water from other rivers and carry it away themselves. For
instance, the Savannah River has stolen a lot of branches from the
Chattahoochee. (See Fig. 177.) Then rivers are young and middle aged
and old, too; torrents first, and then steady-going, and by and by very
mild and gentle; and you might say they are angry when they are in
flood. The Yellow River in China has drowned a million persons in a
year (1887); the Ganges is nearly as bad; and our own Mississippi has
terrible floods.
Fig 177 The
Chattahoochee River Formerly owned the waters quite up to the border of
North Carolina that now flow in the Chateuga and Tugaloo basins into
the Savannah River and so to the sea. It is quite likely that the
Oconee River will capture more of the Chatahoochee waters in times to
come.
Fred. Anyhow they don't mean
any harm, and they are
industrious; they do the best they know how.
Jack. Industrious they
certainly are. In the first place, the water dissolves a great deal of
rocky soil (just as water dissolves sugar) and carries it along to a
new place. Then a river carries a great deal of sand and mud in its
stream and drops that, too, when it can carry it no longer.
pg 197
Agnes. When does it drop the
mud, Jack; when it gets tired?
Jack. You might say so. While
the river is flowing fast it can carry a great deal of mud and sand; as
soon as it begins to move slower some of this mud falls to the bottom.
Tom. If you want to get dirt
out of a wash basin, you have to make the water move quickly. If it
moves slowly, the dirt begins to settle.
Fig 178 The town of
Ems (Prussia) built on the narrow flood plain of the Lahn River
Jack. They say that the
Mississippi carries mud enough every year to make a range of hills a
mile long, half a mile wide at the bottom, and five hundred feet high;
and the Nile brings huge quantities of soil into lower Egypt. The flood
plains of such rivers are the most fertile parts of the world.
pg 198
Fig 179 Niagara
Falls--The falls are 165 feet high, and the river is nearly a mile wide
just
above the falls.
pg 199
The Land.--"When people talk
about the sea," said Jack, "they speak about it as if it were always
changing--they call it 'the restless sea'; and when they talk about the
land they speak as if the land never changed at all--'the everlasting
hills,' they say. Of course it is true that the hills and mountains do
not change much in your lifetime or in mine, and of course it's true
that if you are at the seashore the waves are never still for a moment;
but really and truly the land changes more than the sea does, if you
take the whole history of it. The surface of the land is changing all
the time."
Fig 180 A mountain
range in California--The summits are covered with snow which, melting,
forms the brooks and rivers; rains model the ravines. Every feature of
this landscape has been formed by running water.
Mary. I don't quite see how,
Jack. I have been here all summer. What changes have there been?
pg 200
Jack. You have seen the brook
to-day. What color was the water, Mary?
Mary. Why, it was clear.
Jack. And yesterday, when it
was raining so hard, what color was it?
Mary. It was muddy. Yes, I
see; the rain from the ground carried off some of the soil to the
brook. It was not much, though.
Jack. No, not much. But
suppose you have a hundred showers every year; in a hundred years there
will be ten thousand showers, and every shower will do some work
and will carry away some soil. In a hundred centuries there will be a
million showers; every one of them will do some work, and all of them
together will do a great deal. They will sculpture mountains and level
continents.
Fig 181 Sand mountains
(dunes) in the rainless desert of the Sahara.--They are modeled by the
wind. Along many seacoasts such dunes are to be found.
Mountains.--"Nearly all the
mountains of the globe are modeled by water. Wherever there is frost,
too, great pieces of rock break off and fall. The shapes of mountains
in arid countries like Arizona are modeled by the winds; and then,
pg 201
you know, there are volcanoes, and they change their shape, too.
Everywhere the form of the land is changing."
Tom. If all this went on long
enough, the earth would be flat.
Agnes. You might say more than
that, Tom. You might say that the rains would make all the mountains
flat, and that the rivers would carry everything to the sea. Why
doesn't that happen, Jack? Why isn't all the land carried into the
ocean? Why isn't the whole world flat?
Fig 182 A cliff of
hard rock--The sloping bank at its foot is made up of rock that has
fallen from the cliff.
Jack. If you gave it time
enough, it would be, Agnes; but it would take a great deal of time! The
books say that the surface of a whole continent might be lowered an
inch or so in a century. North America is, on the average, about 2000
feet (that is 24,000 inches) above the ocean, so you see that it would
take at least 24,000 centuries to level it--at least 2,400,000 years.
But long before that time other things would happen to prevent. Some of
the continents are slowly rising out of the sea all the time, and it is
the elevation of whole countries that makes up for the washing away of
the land.
Tom. I never heard of that
before, and I don't understand it.
What countries are rising now, for instance?
pg 202
Jack. Well--Sweden is rising,
slowly rising, two or three feet in a century. And the northern coast
of California is rising, and many other coasts and regions, too. They
say the coasts of Alaska and of Peru have been raised more than
thousand feet.
Agnes. Aren't some regions
sinking?
Jack. Yes, of course. If one
region rises, others will sink. They say the coasts of Massachusetts
and of New Jersey are now sinking about two feet in a hundred years;
and there are plenty of other places, too, but I don't remember them
now.
Agnes. But, Jack, how can
people possibly know that a country is sinking, if it move as slowly as
that? Two feet in a hundred years--why, how can they tell?
Fig 183 Fossil shells
inbedded in limestone
Jack. Well, it is not easy,
but there are ways to do it. If the sinking keeps on long enough, it is
not hard to observe it. For instance, there is a part of the German
Ocean not far from the mouth of the Thames where the whole coast has
sunk. They say you can even see the remains of buildings at the bottom
f the sea when the water is clear. Those were English cities, and the
land has sunk within a few hundred years. We know the history of it, I
believe. There is a very good way to tell, though, what land has risen
out of the ocean.
pg 203
Tom. What way, Jack?
Jack. By seashells--fossil
seashells--found on land, even on mountain tops. Suppose you should
find, not one, but thousands and thousands of seashells on the very top
of a hill; suppose that the whole rock should be made of them. Well,
wouldn't that prove that that particular hill had once been under the
sea?
Tom. Yes, you could prove it
that way.
Jack. Now suppose that all the
hills for hundreds of miles around were made of shells--of shells of
animals that we know cannot live on land, but absolutely must live in
salt water--would not that prove that the region had been under salt
water long ago?
Fig 184 The upland of
New England with Mount Monadnock in the distance
Tom. Yes, of course. Are there
many regions like that?
Jack. Hundreds of them. And in
some of them every bit of the rock is filled with seashells. You know
what sandstone is, of course?
pg 204
Tom. Yes, there is a lot of
its here. Some of our hills are all sandstone.
Fig 185 A mountain in
Utah filled with ravines, every one of which has been modeled by
running water.
Jack. Well, sandstone is
nothing but little grains of sand cemented together to make rock; and
many sandstones have been formed under water--under salt water. A large
river, let us say, brings sand from the shore, and drops the sand
grains on the sea bottom. In time the grains are cemented together, and
then you have layers of sandstone. By and by something like a great
slow earthquake happens, and the sandstone is lifted above the sea. It
may be lifted, in time, very high. Then you have layers of sandstone on
land. The rains come and wear it into ravines, and parts of it crack
and fall, and some of it is covered with soil by the washings of other
rivers.
pg 205
and by and by trees and grass grow there, and you have a country like
the one we live in.
The earth is not solid down to its center, you know. We live on the
outside crust of it. That is solid, of course, and it is about a
hundred miles thick. Inside of the crust great parts of the globe are
red-hot rocks, like melted lava. It is as if the continents and the
oceans were resting on an inside globe of melted rock. The heaviest
parts are always pressing down, and the crust is always being strained
and bent and cracked. Some parts of the earth are sinking very slowly,
and other parts are slowly rising. Wherever the crust moves you have
cracks and when the cracks are large you have long valleys and mountain
ridges. (See the picture, Fig. 188.)
Fig 186 The earth's
solid crust is about 100 miles thick; the narrow line in the picture
would be more than 100 miles thick if the diameter of the circle were
8000 miles. Within the crust the rocks are very hot--melted. The
pressures in the interior are so great that the rocks, though melted,
do not flow like a liquid, but are almost rigid, like a solid.
Stratified Rocks.--"Are all
mountains made in that way, Jack?" said Tom.
Jack. Not exactly in that way,
Tom. You see it is like this: The crust of the earth sometimes breaks
one way, and you have mountains like those in the picture (Fig. 188);
and sometimes it does not break at all, but bends; it may be pressed or
crumpled so slowly that it can yield without much breaking. There is a
way to prove this. Do you know what stratified rock is?
Tom. It is rock layers--in
strata.
Jack. Yes. Now we know that
those layers were, in the first place, horizontal. They were layers of
sand on the bottom of the
pg 206
Fig 187 Model to show
how mountains are made by the cracking of the earth's crust
Fig 188 View of the
mountains formed by the cracking of the earth's crust. (see Fig
187.)--They are in southern Oregon and northern Nevada and California.
The long lakes and the streams lie in the direction of the cracks.
pg 207
sea, or perhaps they were layers of limestone with fossil shells
scattered through them. In the pictures (Figs. 182 and 189) they have
been lifted up so as to keep the layers level; but there are places,
many places, where the layers have been crumpled like this:
(See also Fig. 190.) 
Fig 189 A column of
stratified rock--The rock is made up of nearly horizontal layers. The
softer rock between the column and the cliff has been worn away by the
waves in the course of thousands of years. Fig 182, preceding, shows a
cliff of stratified rock--of rock arranged in layers.
pg 208
The crumpling makes the crust into mountains and valleys, and you must
always remember that just as soon as a mountain is lifted up, it begins
to be torn down again by the frosts, the rains, the earthquakes. The
older the mountain is, the more its first shape has been altered, and
you can tell its age in that way. (See Fig. 180 and 185.)
Fig 190 Strata once
horizontal are sometimes elevated and folded so as to make mountain
ranges, as in the picture, which shows such a case in Maryland. The
Appalachian ridges in Pennsylvania (and the Jura Mountains in
Switzerland) were made in this way.
The oldest mountains in America are the Laurentian Hills, near the St.
Lawrence River, and the Green and Adirondack mountains. The Green
Mountains are about forty or fifty million years old, the geologists
say.
pg 209
Fred. What are the youngest
mountains, Jack?
Jack. The youngest in America
are the Coast Ranges of the Pacific slope. The books say they are about
two or three millions years old. Two million years is young for a
mountain. The Wasatch Mountains in Utah are middle aged.
The Age of the Earth.--"Do they
know how old the earth is?" said Tom.
Jack. It is not known in the
way you can say you know how old a tree is after you have counted the
number of rings in its sawed-off stump; but it is known in a way. Take
these very stratified rocks, for instance. They were formed under water
by sand which settled down on the ocean floor and slowly cemented into
rock. A layer a foot thick will be formed in about 10,000 years, the
geologists say. Then a layer 100 feet thick might be formed in about a
million years, and a layer ten miles thick in about 500,000,000 years.
There is good reason to believe that the earth is at least as old as
that, and maybe older. (1)
Agnes. Five hundred million
years! I shall never be able to realize that! Why, I can't even
understand what a million years is.
Jack. You remember how you
children made a model of the solar system? (2) It helped you to
understand
large numbers, didn't it? Well, you can do something of the same sort
here. Suppose that the next time you walk to the village you play that
every one of your steps counts for a year. When you
(1) There is no part of the earth where we can see
horizontal layers, one upon another, ten miles thick; but there are
places where the layers, once horizontal (---), have been tilted up
(////), so that we can now see their ends and be sure that the original
layers were at least ten miles in thickness.
(2) See Book I (Astronomy), page 20.
pg 210
have taken 125 steps you have gone back 125 years, and that will take
you back to the time of the Revolutionary War (1901 – 1776 = 125); and
when you have taken 1900 steps you have gone back to the time of
Christ. When you have walked three miles you have gone back to the time
when the first pyramids were built. You would have to walk about twenty
miles, each step counting for a year, before you got back to the time
when human beings first came on the earth; and you would have to walk
two or three times round the earth before you got back to the time when
the first life appeared on the earth, and much farther yet to get to
the time when the earth was first formed.
Mary. It is puzzling, but I
think I understand it a little better than I did before.
Jack. Well, my dear, suppose
you remember what we have said and think about it by and by.
Recollect--a step stands for a year; you were born twelve years
ago--twelve steps just takes you out of to the lawn. The Pilgrims
landed 281 years ago--281 steps down the road. You can put a peg here
to stand for the coming of the Pilgrims. Eight hundred and thirty-five
steps will take you to the landing of William the Conqueror in England;
put in a peg for him. A mile will take you back to 600 years before
Christ; the city of Rome was founded about that time. Two miles farther
will represent the time when the pyramids were built in Egypt; and when
you have gone about twenty miles--a year to each step--you will be get
back to the time that men first appeared on the earth. That is far
enough for now. The world was a very old world when Man appeared on it;
it had a long history before he came. There had been life long before
his time, as we know by the fossils,--shells, fishes, and animals; and
there was a long time,
pg 211
nobody knows how long, before that when the earth had no life on it at
all--no men, no animals, not even a plant.
Age of Different Parts of the Earth.--"I
understand how you can tell when the oldest seashells came," said Tom,
"because you would find their fossils in the oldest rocks--in the rocks
lowest down; and if you find a fossil rhinoceros higher up in the rocks
than a fossil whale, you would say the whale came first. But how about
men? Do they find fossil skeletons of men?"
Jack. Sometimes; but more
often they find arrowheads that men have chipped out of flint, along
with the fossils of animals. For instance, there are caves where
arrowheads and lanceheads have been found along with remains of
animals, and where it is plain that the caves were filled up by some
accident soon after the men had died; those men and those animals lived
at the same time. Sometimes they find the bones of the animals split
open, so as to get the marrow out, and blackened with fire.
Age of Man on the Earth.--"Well,
that would prove that the men used those very animals for food,
wouldn't it?" said Fred.
Jack. Yes, and there is a more
wonderful thing still. In one of the very old caves they found bones
carved with pictures of reindeer. The man first killed the reindeer
with his arrows, and dragged him to his cave and cooked him with fire.
Then there was plenty of food in the house. The man felt secure and
happy; he had leisure to think and to enjoy himself. And this drawing
of a reindeer on a bone made by a half-naked savage is the beginning of
all the beautiful pictures in the world. The man was, you may say, our
ancestor; and the drawing is the ancestor of all the paintings of
modern times.
pg 212
Tom. Some one ought to put up
a monument to that man! He was the first artist--long before Pheidias
and the Greeks.
Agnes. How long before, Jack?
Jack. I knew you were going to
ask me that, Agnes. I was sure of it! Well, at a guess, 10,000 years
or, it may be, 15,000. It is not certain, like the date of the last
eclipse, or the time when Rome was founded. It is twenty miles,
Agnes--a year to a step--don't you remember?
Agnes. Yes, I remember; but I
don't see how you can tell, though.
Tom. Why, Agnes, if a man eats
reindeer in order to live, he must be at least as old as the reindeer,
mustn't he?
Agnes. Of course.
Tom. And if the fossil
reindeer are found in rocks that it took 5000 years at least to make,
then the man must have lived at least 5000 years ago. That is the way
they find out.
Fig 191
Jack. That is the way they
find out,--yes, Tom; but you must remember that just about 5000 years
ago, in Egypt, men were building palaces and temples and pyramids,
writing letters to each other, keeping accounts, spinning and weaving,
painting and making statues. You have to go back at least 100,000 years
to find the earliest men. Agnes, there is a place in the West--Idaho or
California, I forget which--where they lately found something very like
a doll; it might have been
pg 213
an idol, but it looked like a doll. Now this doll was buried in gravel
that had been brought down by an old-time river. No one knows exactly
how long it took for the river to bring down all the gravel that
covered the place where the doll was dropped by the man who had it, but
it must have taken thousands of years. Then, long afterwards, the
volcanoes near by sent out rivers of lava, and thick sheets of the lava
poured out and covered the old gravels and dried up the old river. No
one knows exactly how many thousands of years it took for the many
sheets of lava to form one above another; but they were more than half
a mile thick--that we know. Then came a new river flowing across the
lava, and it flowed for so many thousand years that it cut a deep
groove for its bed in the hard lava. Scientific men can make a pretty
good guess how long each of these different things took. Some men were
sinking a deep well in the valley of the new river the other day, and
in the well, deep down, they found the doll. You see that we can make a
pretty good guess how long ago the doll was made by adding up all the
years that were required to deposit the gravel, and to make the lava
sheet, and for the river to cut its way in the lava.
Fig 192 A geyser
spouting boiling water which comes from deep down in the earth
Agnes. Yes, I see. I suppose
that is certainly the oldest doll in the whole world, though.
pg 214
The Internal Heat of the Earth.--"You
were saying," said Tom, "that the interior of the earth is made of
melted rock. I suppose you know that by the melted lava which comes
from volcanoes. Lava is melted rock."
Jack. Yes, it is known in that
way: volcanoes pour out melted rock. And then geysers send out hot
water--boiling water sometimes; and in regions where there are no
volcanoes we find that the deep wells always send out hot water--the
deeper the well, the hotter the water.
Fig 193 The peak of
the Teneriffe in the Canary Islands--The mountain is 12,000 feet high,
and its beautiful form has been shaped by the lava streams flowing down
from the crater. Notice that the rocks in the foreground form part of a
very much larger crater that was active in ancient times and is now
extinct.
Fred. How deep are the deepest
wells, Jack?
Jack. There are some in Europe
nearly a mile deep. They are not dug, you know, but are sunk by boring.
There are deep wells in America, too; one in St. Louis is 3800 feet
deep--more than two thirds of a mile. The water from it has a
temperature of 105 degrees. Boiling water is 212 degrees, you know.
pg 215
Volcanoes.--"You know there are
some splendid volcanoes in Hawaii," said Jack; "papa has seen them. One
of them especially is easy to visit--Kilauea, (1) they call it. It is a
great lake filled with red-hot boiling lava that comes up from some
reservoir of lava deep in the ground. The lava is liquid rock. Usually
it does not flow over the rim of the crater, but sometimes it overflows
and sends great streams of red-hot lava all over the country round
about and even as far as the sea--fifty miles off.
"Vesuvius, near Naples, is the most famous volcano. You know it buried
two whole cities once--Herculaneum and Pompeii." (2)
Fig 194 A volcano is
built up somewhat
as in the picture. Underneath it are old rocks in layers. There is a
reservior of lava somewhere underneath them, and a pipe filled with
lava leading to the surface. (The lava is colored black in the
picture.) When the lava overflows it moves down the side of the
mountain like a great river and covers up everything that comes in its
way. The upper end of the pipe is the vent, and the lake at the top is
the crater. There is often more than one vent. (See the little black
lines in the picture leading to different cones.)
Agnes. Tell us, Jack.
Jack. Pompeii was a kind of
summer resort where the Romans used to go for pleasure. It was a pretty
little town full of fine houses, temples, shops, and so forth, not far
from
(1) Pronounced kee lah WAY ah
(2) Pronounced pom PAY yee.
pg 216
the volcano of Vesuvius.
Seventy-nine years after Christ (A.D. 79) there was a great eruption,
and the ashes began to fall on the city. At first the people were not
very much frightened, but pretty soon things got worse and worse, and
they began to gather up their movables and to leave the city. A great
many of them got away, but hundreds and hundreds were buried in the
ashes and died there. The ashes kept on falling for days, and the whole
city was covered up. Almost the same thing happened in Martinique in
May, 1902. Just imagine what might happen if there were a volcano near
New York, and if the city were to be covered up with a thick layer of
ashes and not even found again for more than a thousand years!
Agnes. Not found for a
thousand years!
Jack. Well, Pompeii was buried
in A.D. 79, and it was not until 1748 that people began to dig there
and found the whole city complete, just as it had been left a good deal
more than a thousand years before.
In a baker's shop, for instance, they found loaves of bread all
shriveled up, and perfumes and oil and jewelry in other shops. The
houses were filled with things that the people used every day;
everything was just as before.
Agnes. But the people,
Jack--were they found? Were their bodies found?
Jack. Their bodies had mostly
wasted away, Agnes; they found their skeletons. One man had come back
after his money, and other people after their jewels. The money and
jewels were found, and the bones of the persons near them. In one place
they found a picture of a watchdog with the sign, Cave canem; that means--what does
it mean, Tom, in English?
pg 217
Tom. It means "Beware of the
dog!"
Jack. Yes; as we should say
"Look out for the dog!" A very great deal of what we know about ancient
pictures and statues we learned from Pompeii.
Fred. If New York were buried
and dug up a thousand years from now, the people of that time would
know how we lived.
Fig 195 The picture shows the volcano of Vesuvius as it
appears today, and in the foreground a part of the city of Herculaneum
after the layer of lava has been taken off. Herculaneum was covered
with thick ashy mud and even better preserved than Pompeii, which was
buried in showers of ashes. Everything in it was found exactly as it
was left--shops, houses, temples, jewelry, tools.
Tom. If you went into a house,
you would know just what each room had been used for--the kitchen and
the dining
pg 218
room and the bedrooms--and just what pictures we had liked and hung on
our walls, and what books we read, and everything of that sort.
Mary. And they would know what
games we played--tennis and golf; and they might find Agnes' dolls and
mine.
Agnes. Just as we found the
doll Jack told us about that was buried under the lava in California.
Fred. Are there any volcanoes
in the United States?
Jack. There are plenty of
mountains that are old worn-out volcanoes, and a few that are still
active. Mount Shasta, for instance, in California, is an old volcano,
and there are active volcanoes in Alaska, Hawaii, and the Philippines.
You children ought to recollect, every time you look at a map, that a
very large part of three great states--Washington, Oregon, and
Idaho--is nothing but an old lava field. A good part of the lava is
3000, even 4000 feet thick, and it covers thousands and thousands of
square miles. All that lava flowed from ancient volcanoes, though it
did not flow all at one time; for they find the lava in layers with
ashes and soil between, and in some of the soil they find petrified
tree trunks.
Tom. That shows the trees had
time to grow between one lava flow and the next one, doesn't it?
Jack. Yes, and it gives you an
idea how long it took to deposit all that thickness of lava. The doll I
told Agnes about was found in this very lava field.
Earthquakes.--"Do earthquakes
come from volcanoes?" said Fred.
Jack. There are always
earthquakes wherever there are active volcanoes, Fred. You can see that
a volcano in eruption which has energy enough to throw huge stones
thousands of feet into the air must shake all the ground near it by its
pg 219
explosions. All volcanoes make earthquakes, but very many earthquakes
are not caused by volcanoes.
Mary. What does cause them
then, Jack?
Jack. Suppose you lay a book
flat on its side, Mary, and imagine that the book is part of a layer of
rock that was once deposited at the bottom of the sea. Now take another
book and lay it flat on the first one. That stands for a second layer
of rock--perhaps a different kind of rock--lying over the first layer.
Now you know the crust of the earth is moving slowly all the time,
sometimes up, sometimes down. Suppose both those layers of rock were
lifted so that one end of them was higher than the other. Tilt the
books, Mary, and keep tilting them, and see what happens.
Mary. Why, one book slides off
the other. (1)
Jack. That is exactly what
sometimes happens to great beds of rock. They lie flat in the first
place. Then they are slowly tilted, and by and by one of them slides a
little--a very little--on the other. Ten million tons sliding only a
little way--an inch perhaps--will make a terrible shock that can be
felt for hundreds of miles around. The Charleston earthquake was caused
in just that way.
The geologists say that the layers of rock underneath South Carolina
lie one on another like the two books, and the earthquake was caused by
the sliding of the layers. The rocks I am talking about were deep
underground, you know. When they moved, the rest of the rocks moved,
too, just as a pile of bricks will slide when you move some of the
bottom ones; all of them moved. A good part of Charleston was wrecked,
you know, and all the eastern part of the United States was shaken
(1) The simple experiment should be tried in the
schoolroom, choosing two
books with smooth covers.
pg 220
more or less. Why, they even felt the shock at Boston, at Toronto in
Canada, at Chicago, at St. Louis, and at New Orleans. The shock was not
severe there, but it was felt.
Fig 196 The church of
Saint Augustine in Manila, Philippine Islands, after the earthquake of
July, 1880.
Tom. Of course an earthquake
is weaker and weaker the farther you go away from the center of it.
pg 221
Fig 197 View of part
of Charleston, S.C., wrecked by the earthquake of August, 1886
Jack. Yes; like the little
water waves in a pond when you throw in a stone. That is a
"waterquake," you might say. You know the waves are larger and higher
at the center, and become smaller as they move out. All of South
Carolina was badly
shaken, so that chimneys fell. The shocks were strong enough to
frighten people in Georgia, in Ohio, and in
pg 222
Pennsylvania, and they were felt as far as the Mississippi River, and
farther.
Mary. Were many people killed,
Jack?
Jack. Only a few, Mary. They
ran out of their houses, and lived in the parks for several days till
the shocks were over.
Agnes. Oh, did the earthquake
last for days?
Jack. There were shocks every
now and then for several days, but only a few really severe ones. You
see it took several days for all those rocks underground to settle down
and be quiet. There was an earthquake in the Mississippi Valley once
(1811) that lasted nearly a year. The people camped out of doors for
months and months.
Agnes. Might we have an
earthquake here, Jack?
Jack. Certainly, we might; no
one can tell. There are not many earthquakes in the eastern part of the
country, and those that we have are usually light; you need not be
afraid of them. If an earthquake comes, go out of doors and keep away
from houses--that is all. But there are earthquakes everywhere--light
ones. You boys can prove it if you want to.
Fred. How can we prove it?
Jack. Get some pieces of nice
wood--red cedar, for instance--and make two or three pyramids. (See
Fig. 198.) Then cut off a little of the top of each one of them, and
stand them upside down in a steady place--on the mantelpiece of a room
that is not used much, for example. When a slight earthquake comes--one
too slight for you to feel perhaps--the house will be shaken and the
mantelpiece, too, and the pyramid will fall on one of its sides. Try it.
The boys did try it. They made half a dozen pyramids and cut off a
little of the top of each one, and stood them about in different places
in the house and in the barn. They
pg 223
often would find one of them fallen on its side, and they usually
discovered that the housemaid, in dusting, had caused that particular
earthquake. But every few months they found all the little pyramids
thrown down, and most of them lying in one direction; and then they
knew that there had been a light shock--too light for them to feel, but
strong enough to overturn their "earthquake detectors," as they called
them. The direction in which the detectors lay on their sides showed
the
direction in which the earthquake wave was moving--north and south, for
instance.
Fig 198 Pyramid
The Lisbon Earthquake.--"They
say the Lisbon earthquake was one of the very worst," said Tom; "do you
know about that, Jack?"
Jack. It was one of the worst
certainly because there was not only an earthquake, but a great sea
wave too. The people ran out of their houses to take refuge in the
churches, and then the churches fell and crushed them. Many went to the
wharves
pg 224
so as to be away from falling walls, and a huge wave from the
sea--eighty feet high, they say--rolled in and drowned thousands of
people.
Fred. A wave eighty feet high!
What made it, Jack? Was it a part of the earthquake?
Jack. No doubt the level of
the sea bottom was changed somehow, and the water rolled in like a
great wall. That often occurs in South American earthquakes. A strange
thing happened to one of our war vessels once. It was the Wateree, and she was at anchor in
the bay of Iquique (1) in Peru (1868). All of a sudden came a great
wave
from the sea and tossed the ships about like boats, and it carried the Wateree far inland and left her
there high and dry. Think of it--one of our war ships with all her guns
and men (no one was hurt) high and dry on land!
Fred. What did they do? Could
they get her off?
Jack. No; and so the
government took away all her cannon and everything that was valuable,
and sold her to a Spanish gentleman for a summer house!
Agnes. I think that's funny. A
man-of-war for a summer house!
Jack. That is not the funniest
part of it, Agnes. A few years later there came another great sea wave,
and it lifted up the Wateree and carried her a long way farther inland,
and there she is now, a summer house for a different family.
(1)
Pronounced ee--KEE--kay.
