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.