Now, I can very well remember when I first saw a coal fire, and how odd it looked to see what seemed to be burning stones. For, when I was a little girl, we always had logs of wood blazing in an open fireplace, and so did many other people, and coal was just coming into use for fuel. What should we have done, if everybody had kept on burning wood to this day? There would have been scarcely a tree left standing; for think of all the locomotives and engines in factories, besides all the fires in houses and churches and schoolhouses. But God knew that we should have need of other fuel besides wood, and so he made great forests to grow on the earth before he had made any men to live upon it. These forests were of trees, different in some ways from those we have now, great ferns as tall as this house, and mosses as high as little trees, and palm-leaves of enormous size. And, when they were all prepared, he planned how they should best be stored up for the use of his children, who would not be here to use them for many thousand years to come. So he let them grow and ripen and fall to the ground, and then the great rocks were piled above them to crowd them compactly together, and they were heated and heavily pressed, until, as the ages went by, they changed slowly into these hard, black, shining stones, and became better fuel than any wood, because the substance of wood was concentrated in them. Then the hills were piled up on top of it all; but here and there some edge of a coal-bed was tilted up, and appeared above the ground. This served for a hint to curious men, to make them ask "What is this?" and "What is it good for?" and so at last, following their questions, to find their way to the secret stores, and make an open doorway, and let the world in. So much for the fuel; but God meant something else besides fuel when he packed this closet for his children. At first they only understood this simplest and plainest value of the coal. But there were some things that troubled the miners very much: one was gas that would take fire from their lamps, and burn, making it dangerous for men to go into the passages where they were likely to meet it. But by and by the wise men thought about it, and said to themselves, We must find out what useful purpose God made the gas for: we know that he does not make any thing for harm only. The thought came to them that it might be prepared from coal, and conducted through pipes to our houses to take the place of lamps or candles, which until that time had been the only light. But, after making the gas, there was a thick, pitchy substance left from the coal, called coal-tar. It was only a trouble to the gas-makers, who had no use for it, and even threw it away, until some one, more thoughtful than the others, found out that water would not pass through it. And so it began to be used to cover roofs of buildings, and, mixed with some other substances, made a pavement for streets; and being spread over