have taken place very slowly. Mountains have been raised, and whole
continents have been sunk by movements so slow that if the hands of a
clock went only once round the dial in a year the hand would go faster
than these mountains have risen or the continents sunk. Almost always
whenever there has been sudden and _violent_ action it has been near
volcanoes or during earthquakes; but these things, terrible as they
are to the people living near, disturb only a very small part of the
surface, and such violence neither buried the coal beds nor raised
the slate hills of Wales. Many of the small effects of the internal
force of the earth have been sudden and violent, but the greatest and
grandest have been slower than anything we can imagine.
If this had not been so, we should not find fossil shells just as they
sank quietly to the bottom of ancient seas, quite undisturbed. We
should not find delicate ferns and insects with all their breakable
parts perfectly preserved, and as lightly laid as if you had put
them away carefully in a cabinet upon cotton wool. Yet many of these
have sunk down hundreds of feet below the open air where they _must_
have lived. We find the ripple marks of the waves on old sandstones,
and even the prints of the feet of birds and animals as they walked
upon that rock when it was soft sand, and the little pits made by
rain-drops on the moist earth. All this speaks of stillness, and
gentle movement, no violence. So slowly and softly have these rocks
settled down, that we can read in them the history of the life that
was. But if there had been any sudden and rough movement all these
fossils might have been broken up and we should have had nothing but
fragments, and the “puzzle of life” could never have been put together.
Nature’s forces are immense, but they work slowly, irresistibly, and
majestically.
THE ICE AGE.
We have seen now what the principal rocks are made of and the way
in which their places have been changed by upheaval and depression.
Water, as we know, has been at work and has done great things in _all_
ages of the World’s history. I have called it “one of Nature’s most
powerful tools,” and when we look at the quantity of chalk alone that
there is in the world, and remember that this was all laid down in
water, and perhaps a great part of its lime carried down by rivers to
the seas where it settled to the bottom, after the corals and small
shell-fish had worked it into their bodies, we are right in thinking
water a great Magician indeed. Why, even so small a river as the Thames
carries down to the sea every year as much dissolved earth as would
make a good large hill; and what must such rivers as the Nile, the
Amazon, the Mississippi, and the great Chinese rivers do! There must
have been gigantic rivers, too, in the old times, or else it would have
been impossible that the deep sandstone and slate beds could have been
formed; for these are all laid down by the washing away of earth in
water.
Ice, which is only solid water, has also been a powerful tool in
shaping the surface of the Earth, but it has not been _always_ at
work as water has. Ice now covers only a comparatively small part of
the globe near the north and south poles, and mountains like those in
Switzerland; but by watching what ice is doing now in these places we
are able to be certain that there has been a time when it covered
Scotland, Cumberland, Wales, Sweden and Norway, and nearly all North
America. In watching the great “rivers of ice,” called glaciers, in
the Alps, for instance, we see that they slip down from the mountains
slowly, creeping on year by year, and bringing with them pieces of
rock and stones. We see also where they have melted that they have
been grinding the rocks beneath them with their great weight, and have
cut grooves into, and scraped and polished the hardest granite. The
stones underneath the glaciers have been pressed so heavily upon the
rocks that they have left deep marks, and we find the same kinds of
marks and heaps of stones in many mountains where there are no glaciers
now. There are other things too which convince us that a great ice
sheet spread over almost the whole of Great Britain. When the huge
icebergs break away from the frozen shores of Greenland and North
America, they often have frozen into their ice large blocks of rock,
sand, gravel, &c., and when they drift into the warmer seas of the
south they melt, and of course these blocks or “boulders,” as they are
called, sink to the bottom. Just the same kind of boulders are found
in many parts of the world, where icebergs never come now, and as they
are of a different rock from that on which they lie, they must have
been brought there somehow. We naturally suppose then that they were
brought by icebergs. Sometimes boulders of granite have been found thus
among clay, many miles from where there are any granite rocks on the
surface, and there can be no doubt that they were originally frozen
into an iceberg, which floated away with them and when it melted left
them so far from their native place. In many of the midland and eastern
counties once floated these icebergs, dropping the stones and boulders
which they brought away from the Welsh, Cumberland, and Scottish
mountains.
The climate of the earth must have been fearfully cold when our country
was covered with ice, just as Greenland is now. Geologists suppose that
there must have been more than one age of ice, and that between these
ages the climate of the world was pretty much the same as at present,
although it is certain that there were periods when England was much
warmer, because many of the fossil plants could not have grown in a
cold climate.
You will want to know whether there were any land animals living during
the ice periods. It is impossible to be quite certain, but it is most
likely that the mammoth was living both before and during the _last_
ice age, because its bones have been found among the earths brought
down by the glaciers.
I have said all you will be likely to remember at present about the
nature of the different rocks, but it will help you to understand
better how they have been laid one upon the other, and how they have
been moved and broken by upheaval and subsidence, if you look at the
drawings on page 51.
DENUDATION.
It has often happened that some of the harder and older rocks, like
granite and slate, have pushed themselves through those earths lying
above them, and then the sea or a great river has washed away all the
earths from one side of the rock. The rain, too, falling for thousands
of years, has swept them down into the valleys and mixed them together.
This is called denudation, or “laying bare” the harder rocks by washing
the softer ones away from them. Those beds of pebbles on the sea shore
also have been battering against the rocks for ages and very gradually
wearing them away, as you can see if you watch the stones being driven
into and sucked out of holes and cracks by every wave. Thus, both
the loose stones and the solid rocks get polished and ground away,
and Nature is always destroying and making again by turns. If this
destruction went on continually without any raising of the land to make
up for it, the surface of the whole Earth would in time become level;
but old sea beds are always being slowly raised above the water and
prepared for the growth of plants and the habitation of animals.
[Illustration: _Upheaval._]
[Illustration: _Subsidence._]
[Illustration: _Denudation._]
If you watch the little rills of water on any rainy day, trickling
down a hill, or the springs which bubble up at the foot of cliffs on
the sea shore, you will see an example of denudation in a small way.
The earth is washed off the surface here and there, and carried down
and laid up in banks in some places, and the harder ground underneath
is laid bare. Little beds of stones are collected in one place, and
sticks and straws and such light things in another, and this is just
what has been done on a large scale in mountain regions, all over the
world for many centuries.
In the uppermost sketch on page 51 you will see how the granite has
been lifted up with the layers of other earth along its sides, and
afterwards even layers have been deposited above; in the second there
has been a great crack in the land, and a great mass of rock has
subsided, and the hollow has become filled up in time with clay, and
mould, and rich soil, so that some one has built a house and made a
garden on it; in the third the river has cut a gorge in rocks which
were once continuous from cliff to cliff, wearing away the softer
earths more easily than the harder. If the Earth was cut into in
different places we should find the rocks arranged in a very similar
way to that in the three sketches.
BOILING SPRINGS, ETC.
In several different countries there are very strange sights, but
scarcely anything is more astonishing than the fountains of boiling
water which shoot up out of the ground. There are a good many of them
not far from us, in Iceland, and many hundreds in Wyoming in America,
and they are called “geysers.” Steam and boiling water, and sometimes
mud, are thrown up by these natural fountains to a height of 200
feet—as high as the top of the spire of a church. The water must come
from a great depth in the ground—perhaps many thousand feet down—where
the heat is intense. This water springing up with clouds of snow-white
steam, and falling all round in showers, has a most beautiful
appearance. These geysers now and then throw out very little water,
just bubbling up above the ground, and then travellers boil eggs and
chickens and such things in them, and have a pic-nic near them. It is
impossible to say how long they have lasted, but we know from history
that some have been spouting out water for at least 2,000 years, and
how much longer no one can tell. They may have something to do with
volcanoes, because water may have found its way to the heated interior
of the earth, and being converted into steam, expands and causes an
eruption.
Now that we have some idea of the construction of the Earth, we must
go on to the _life_ of the wonderful plants and creatures which have
peopled it.
_THE VEGETABLE PART._
THE DAWN OF LIFE.
The first beams of the rising sun, and the first grey light of the
morning, tell us of the coming day; but we cannot even think of the
dawn of that far-off day in the Earth’s history, when no voice of man
or beast was heard, and no trees or grass covered it, without solemn
wonder at the immense distance that day is from us. A thousand ages are
in the sight of the Creator but as yesterday, and the period of man’s
existence is only a moment compared to that of the lowly creatures
which built up this World for him. In the first seas and on the land
nothing was heard but the rushing of waters and the roaring of the
fires of volcanoes.
It is impossible to be quite certain whether the first living things
were animals or plants; but I think it most likely that very simple
plants grew first, and that very simple animals came after or with
them. Among the first of these, or perhaps the very first, were some
small animals called _Eozöon_, which means the “life-dawn animal,” and
with them grew some simple plants. On the banks of the St. Lawrence
river in Canada there is a great bed of rock called the Laurentian
rocks, made almost entirely of the tiny remains of the “life-dawn
animal,” which, when we look at them through a microscope, are found
to possess nearly the same structure as some lowly organized shells
living in the seas now. These rocks are found in many parts of the
world besides—in Eastern America, Bavaria, Scotland, and Norway; and
in some places their thickness has been estimated at thirty thousand
feet, or nearly six miles, or one hundred times as thick as St. Paul’s
Cathedral is high! These little creatures you see were at work over a
great part of the Earth’s surface, and you may fancy how many thousands
of thousands of years it took them to build up these rocks. The
“life-dawn animal” is far older than the chalk-building foraminifera,
and so far as we know it lived alone in its seas. There were none of
the beautiful twisted _ammonite_ shell-fish, nor the shark-like fishes
of the chalk seas. The eozöon was the only kind of living creature, the
“lord of creation” for the time; and though storms raged in the seas it
inhabited, the water was so deep that it lived on undisturbed. When you
are able to use a microscope you will be able to see the traces left by
these tiny animals in what is now hard stone.[1]
Life began in a very small way: there were none of the great land
animals we have now; but these seemingly insignificant builders were at
work so long that they made the immense rocks I have told you of. But
this is not all. About this time some very simple plants grew on the
land, and were carried down by the rivers and formed deep beds. After
a long time these became covered up with different earths and were
turned into the substance called “black-lead,” which you use in drawing
pencils. But this is not really lead; it is almost pure carbon—in
fact, the oldest kind of coal—so old that it will not now burn like
coal, and is entirely made up of fossil plants crushed out of shape, so
that we cannot now trace their forms, as we can the plants of the coal.
When then you next take up a drawing pencil it will be easy to remember
that the black substance which marks the paper was once a living plant,
now changed by heat and pressure into almost pure carbon. As the name
eozöon has been given to the “life-dawn animal,” I will give this
black-lead the name of _Eodendron_, or the “dawn-plant.”[2]
Two very simple forms of life then occupied the earth and sea at the
earliest time when anything at all was living, and strangely enough we
use the dead bodies of both of them. We build houses of the rocks the
eozöon laid down at the bottom of the sea, and the beautiful art of
drawing is carried on with the carbon from the first plant life of the
world—the eodendron.
I must take you away presently to the coal, and sandstone, and chalk,
and show you how plants and animals gradually increased in number and
size, and fishes began to inhabit the seas, and all living things were
slowly going on to greater perfection; for as time went on there was a
steady progress from creatures like the eozöon, which had scarcely any
power of moving about, to the active, quarrelsome and greedy things
like crabs and lobsters which came after them, and the gigantic ferns
of the coal beds. The peaceful “life-dawn animals” drew their food from
the vegetable substances dissolved in the waters, though they perhaps
also lived on animals still smaller than themselves; but, by-and-by,
creatures, which must have been monsters to them, swarmed in the seas
and devoured their smaller companions wholesale; and in time the Earth
became very much the same as it is now, a place where the struggle for
life is always going on. It is certain that animals have fed upon one
another from the very beginning; but this is no doubt a wise law of the
Creator to prevent them from increasing too fast, as they would do if
all that were born lived, and none were destroyed.
We know much less about the vegetation—the plants and grasses—of the
early ages of the world than of the animals; because plants rot away
faster than bones and shells, and, besides, are less likely to be found
in places where they would be preserved. A dead tree might be eaten up
entirely by insects, as the white ants eat up fallen trees in a short
time in tropical countries, and what is left of them crumbles away to
fine powder and mixes with the soil. Immense trees are thus devoured
now by millions of tiny insects no longer than your thumb nail, in
India and Australia. No such thing as a whole and perfect fossil tree
with every twig and leaf has been found; but then the coal beds are
really great forests which have been buried for so long a time that
they have quite altered in appearance. Still, among these coal beds we
often find the bark, fruit, stems, and branches of trees very much like
firs, and ferns, and huge club-mosses, which have the same shape they
had when living, though they are quite black, and burn exactly like
coal.
But there were plants long before the coal forests lived, and many
fossil sea weeds are found in the old sandstones and limestones in
Wales and other places.[3] The Old Red Sandstone, whose position you
can see below the coal in the table of succession of formations, page
42, does not give us many fossil plants, though fishes and shells are
common. This rock is found in Scotland, Herefordshire, Devonshire, and
Ireland, as well as other places, and is often more than 2,000 feet
thick. It was not all formed in salt water we know, because many of the
fossil fishes and shells it contains are fresh water kinds. It must
all have been made of the pieces of still older rocks worn away by
rivers and settled like a sediment in immense lakes, some of which were
fresh water. Then, after the Old Red Sandstone, came a time when the
limestones below the coal were laid down at the bottom of a vast sea,
and here the remains of land plants are of course few. Then it seems
there must have been a very long time when there were large continents
all over the world raised above the seas, but not very much, and on
these the forests grew which afterwards became coal fields. Until this
time the plants had been mostly water weeds, reeds, rushes, and sea
weeds, and it was not until England and Ireland became one continent,
as they were once and covered with woods, that the great period of
vegetation began.
The growth of plants was then most wonderful; but although coal is
found in many different parts of the world, it was not all formed at
one time, and though it is plentiful in England and Wales, Scotland,
Ireland, France, Belgium, Russia, Hungary, Australia, New Zealand,
China, and Borneo, it is older in some countries than in others. It
is fortunate, however, that this useful material was made in Nature’s
workshop in so many different countries, or it would have to be carried
from one to another. The coal forests were not the same trees as we
have now—oaks, elms, ashes, limes, and so on. Most of them had rather
hollow trunks and splendid waving tops like ferns and reeds, though
there were some like our fir-trees.
If you lie down in the long grass before it is mown, and look through
the stalks and fancy yourself an inch high only, you will have some
idea how the coal forest would have looked if you had lived then.
But there were no human beings on the Earth then, and I do not think
there were any large animals, at least none have been found in the
coal itself, except in Switzerland, where a few bones of the mammoth
(an ancient elephant) and of the rhinoceros have been discovered in
the much newer beds of coal, and also those of a large reptile like a
crocodile in the coal beds of Ohio in America.
[Illustration: II.
_Fossil Tree Fern._
_Calamites._
_Lepidodendron._
_Different Kinds of Plants of the Coal Forests._]
In such immense forests insects must certainly have been plentiful,
and some of the fossil bodies of beetles, dragon-flies, and spiders,
have been preserved, and a few tree lizards.[4] Of course the edges of
the coal forests were washed here and there by the salt sea, and
there must have been some fresh water rivers and ponds, for we find
both fresh and salt water shells in these beds. It was almost dark in
these forests, so thickly did the plants grow together. There were
enormous club-mosses close together and as high as most houses, with
their leaves interlaced making a complete network to shut out the sun.
But the sun which shone on the forests was warm, and the air which went
through them was soft, or they would not have grown so wonderfully.
Indeed, there can be no doubt that the climate of northern regions was
once much warmer than it is now. A thick bed of coal was discovered
by the Arctic Expedition in 1875-6 actually within five hundred miles
of the North Pole, where the ice on the sea is now thirty or forty
feet thick![5] The forest which formed this coal could only have grown
in a temperate climate, and there are no forests there now; it is so
intensely cold they could not live. There must then have been a great
change in the climate of the Arctic regions since that coal was living
vegetation. The few plants and mosses which can live there now are of a
very different and more hardy kind than those of the coal forests.
If you look at the engraving facing page 64, you will see a drawing of
one of the tree ferns with its delicate fronds which grew so abundantly
in the coal forests, and there are many other plants, some like the
common “mare’s tails,” or _calamites_, growing in shallow ponds and
ditches now—only the “mare’s tails” or calamites of the coal forests
were as high as poplars.[6] You can imagine what a splendid sight these
forests of ferns, club-mosses, and “mare’s tails,” must have been, and
what a multitude of beautiful insects and butterflies must have flitted
about in them; but their frail bodies have almost all perished, so that
we know very little of the animated creatures of the time.
Besides several sorts of coal both soft and hard there is a substance
called “lignite,” which is scarcely wood and scarcely coal, of a brown
colour. In fact, lignite is wood almost turned to coal, and it has
helped us to learn that coal was once living wood; but it is not nearly
so old as the coal. Then again there is the beautiful substance called
“jet” used for making bracelets. This is a kind of fossil gum or pitch
dropped from the trees while they were growing, and, though different
in colour, it is much the same in kind as amber. Amber is often found
with flies, spiders, and small leaves imbedded in it. When this fossil
resin or gum was flowing out of the ancient pine-trees, and was quite
sticky, flies settled upon it and became entangled in it, and as more
of the gum flowed out they became quite covered. Then the gum dropped
from the tree and hardened, and it is now found in lumps on the shores
of the Baltic Sea, and in beds of sand and clay with fossil wood. It is
of a beautiful bright yellow colour, and beads for necklaces and other
ornaments are made out of it.
If we arrange the things we have been talking about in order, the
oldest first, they would come thus: plumbago or black-lead—or, as I
have called it, eodendron, “the life-dawn plant”—first, then hard coal,
then soft coal, then lignite and jet, then bog oak and peat. But I
must tell you something about bog oak and peat. In many of the swamps
and bogs of the World the trunks of dead trees are found, which have
become quite black and almost like lignite, because they have been
buried so long. Thus, in the bogs of Ireland oak trees are often found,
and they were most likely living when the reindeer inhabited Ireland.
This old bogwood is made into beads for necklaces and other ornaments.
Peat is a partly decayed vegetable substance, with beautiful little
plants growing on its surface, and is really coal in its infancy. It
is found all over the world more or less in wet places, and consists
of the roots and stems of mosses and reeds, some of which are like
the gigantic plants of the coal period, but very small in comparison.
I have no doubt that in time some of these peat bogs may be turned
into coal if they sink down and become covered with other earths, but
at present they are all on the surface and so soft that they are
dangerous to walk upon because one may sink in and be smothered.