Part 6

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.

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.

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.”

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. 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.

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. 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! 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. 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.