However, one day, before I had made more than an opening to my tunnel, I listened to a conversation about digging deep wells and mines. I could not understand most of what was said, nor did I know the meaning of any of the long words which I then heard for the first time; but there was one thing which I did understand, and this made me stop short in my work, afraid to dig another spadeful of earth. I had thought it would be so delightful to walk through my tunnel, and come out at the other side where the strange New Zealand people lived; but now my great dread was lest I should get to the inside of the earth before I was aware of it, when I had dug perhaps only a little hole; for those who were speaking about it, said how impossible it was to get very far below the surface,—or, as they called it, very deep into the "crust" of the earth—because of the great heat, which makes the men who work in deep mines glad to throw off their clothes. "The deeper the bore, the greater the heat," they said; and then went on to speak of this crust as if it covered the earth as the shell covers an egg, so that I thought it might perhaps be broken just as easily. "And how dreadful it would be," I said to myself, "if I could get to the inside of the earth and find it all on fire!"
It was a pity that I did not ask a little about what surprised and frightened me so much, and especially that I did not get someone to explain to me the meaning of this new word, the "crust" of the earth. I know now that it is the name that has been given to that part of the earth which is known to be firm and solid—the bed of the ocean as well as the dry land. Beneath this crust lies the inner part or kernel of the earth, and no one knows of what it consists; all that can be done is to examine the rocks which rest upon it, and whether the lowest of these layers of rock has yet been reached, we do not know. If you have ever been to a quarry where the rocks have been blasted and cut away, you have seen a little way down into this earth-crust. I remember once, when I was living in a country warmer than England, seeing a beautiful sight. It was a great quarry in a hillside. In part of it men were busy, cutting out the stone and carrying it away; but all over one side, which was no longer worked, a beautiful vine had woven its lovely green leaves and purple clusters of grapes.
You would have thought, perhaps, that the side where the rough, hard rock was hidden by the fruitful vine, was the only part of the quarry worth looking at; but the other side, where the quarrymen were at work, was very interesting to anyone who would take the trouble to notice how the rocks lay, piled one upon another, and especially to one who had learnt a little about the different kinds of rock of which the earth-crust has been made. Even if you have never learnt much of what is called geology, by keeping your eyes open and your mind awake you may see a great deal in the stones which have perhaps seemed to you most uninteresting. A block of granite from one of the Dartmoor hills, and a piece of slate from a Welsh quarry—how different these two kinds of stone are! We see this at once; but they become much more interesting when we know that each has its own history. The granite is one of the fire-made rocks, so called because there are marks upon it, like letters written long ago, quite plain to those who have the skill to read them; which show that though it is now so hard, it was once soft, as soft as iron becomes when melted by very great heat. The mountains of Devon and Cornwall, the Grampians of Scotland, even Mont Blanc, the "Monarch of Mountains," are made of the grey or red granite which takes such a beautiful polish when cut that it is much prized for buildings.
The piece of slate has quite a different history. It is one of the water-made rocks, in which so many fossils have been found; while in the fire-rocks there are no remains of anything which ever lived. The water-rocks are so called because water has had so much to do with the making of them; for they have been very slowly formed by the gravel and grains of sand which have been washed down by streams and torrents, and left behind in their course. In these slate and sandstone rocks the wonderful fossil animals, which are to be seen in the Museum, have been found. A fossil means what has been dug out of the earth; and numbers of animals are to be found buried deep in the rocks along the coast of Yorkshire—huge creatures which lived on the earth long, long ago, of which the hard parts, such as bones and teeth, have gradually been turned into stone.
All this is very wonderful to think of, and I am sure the poet, who spoke of finding "sermons in stones," was wiser than he knew; but what will you say when I tell you that one kind of rock—the chalk with which you are so fond of drawing upon the black-board—is made of shells, most of them very tiny ones, which can be seen only by a microscope? What myriads of living things once made their homes in those little shells, and what sort of life they lived, we cannot tell; but there the shells remain in the white chalk, and the microscope will show them to you, as it shows so many hidden wonders in this wonderful world, where the very great and the very small meet on every hand.
Only the other day, May brought me a lovely branch of white coral. "Look," she said, "when baby was out for a walk, a lady gave her this." She thought it very pretty, but she was surprised when I showed it to her through a magnifying-glass, and told her that it had been made by a very tiny kind of jelly-fish; a plant-animal some people call it, of the same kind as the sea-anemone; and she wondered still more when we found in a book a picture of a coral island, and I told her that such little creatures have been busy ever since the world began, constantly building up the coral-rocks. These rocks, which are strong enough to resist the force of the waves, rise out of the sea naked and bare, but are soon covered with green, and become the resting-place of the sea-birds, until at last they are like that lovely island, fringed with tall cocoa-palms, which we saw in the picture. If it were not for the myriads of tiny jelly-fishes, who work on and on, each forming its own little bones from the lime it gets from the sea-water, dying, and leaving its skeleton behind for others to build upon, there would be none of these beautiful green isles of the sea of which sailors love to tell us.
We were speaking of contrasts some time ago; now for a contrast. Beside the coral, with its lovely branching sprays, we will put a piece of coal. You think the coal very black and ugly, not fit to be put alongside the white coral; but let me tell you that there is that in the coal which was once far more beautiful than the coral—which is only a bare skeleton after all—could ever be; for, though coal and coral are alike dead now, both were once full of life.
But the coal, which is certainly more useful than beautiful at present, has had a wonderful past. Besides the fossil-animals which are dug out of the earth's crust, there are also fossil-trees and ferns, and it is of them that coal, which seems only like a black stone, is made. I have read that in a part of England where there are now great coal mines, for a long time no one knew the worth of coal except some old women, who said they could make their fires burn beautifully by putting those black bits of stone upon them. How strange this seems; and what should we do now if we had not these black stones to burn? Coal is generally called a mineral, as all things which are dug from mines are called; but it is really a vegetable. You may perhaps pick up in some swampy place, a piece of wood, very black, which breaks as you handle it. Look at it well, for this wood is being turned into coal; but for what was once a forest to become a coal-mine takes a very long time indeed, with a strange history of change and decay; yet it is true that the coal dug out of mines is nothing else than trees and ferns and mosses, long ago buried by mud and sand, and so crushed together that they have become like a piece of black stone.
The other day Chrissie had what you would consider a rare treat, for his father took him and his brother down a coal-mine. They put on some of the miners' clothes, and then got into the "cage," and were let down by a strong chain; down, down, until they reached the bottom of the shaft, as the tunnel from the mouth of the coal-pit to the place where men are at work below is called. I have never seen a mine of any kind, but if I ever find myself at the bottom of a coal-pit, I think I shall use my eyes, and see whether, even in such a grimy place, I cannot find something beautiful. I shall hold my safety-lamp high, and look carefully at the roof and sides of the mine, for I have been told that in all coal-mines remains of the plants from which the coal is made are to be found; so I should not be surprised to find here and there in the dark shining walls traces of leaves and branches; and upon the hard clay which forms the roof, beautiful patterns of ferns, which lived long, long ago, and have lain buried for ages.
"In a valley, centuries ago,
Grew a little fern-plant, green and slender,
Veining delicate and fibres tender,
Waving in the wind, crept down so low;
Rushes tall, and moss, and grass grew round it;
Playful sunbeams darted in and found it;
Drops of dew stole down by night and crowned it;
But no foot of man e'er came that way,
Earth was young and keeping holiday."