Coal is very common, and everyone knows what it looks like and what it is used for. It is a hard, black substance, like a stone; but it burns well, and gives off great heat. So it is chiefly used as fuel for fires to keep our houses warm in the cold weather, and to burn in engines to make steam. But coal has also other uses. Coal is used in power stations to produce electricity, for lighting houses and streets, and coal-tar, a black oily liquid that is pressed out of coal, is very useful in many ways. The tar is used as a paint to preserve wooden ships from rotting, and from it is made beautiful dyes for coloring cloth, sweet scents, and some very good medicines.
Coal is found deep under the ground in certain kinds of rocks. To get it out, deep mines have to be sunk; and men, called miners, go down into the mines and dig the coal out of the rock and send it up to the surface.
Coal is a very common thing but it has a wonderful history, In fact, the story of a lump of coal is like a fairy tale. Coal looks like stone, but is really wood. It is wood that has been pressed under the great weight of rocks for thousands of years till it has become a sort of rock.
Long, long ago great forests of trees grew in different parts of the world especially in the north of England, in parts of Germany, in America, and in India. After a long time, the land slowly sank, until the sea flowed over it and killed all the trees. The land with the dead trees went on sinking, until it became the bottom of the sea. The rivers washed into the sea every year with great amounts of sand and mud, which covered up the dead forests. The sand and mud went on piling up, until their great weight turned them into rock. Then the bottom of the sea slowly rose again, until it became dry land once more and the sea was driven back. Underneath that great weight of rock, the trees of the old forests were slowly pressed into coal, which lay in what is called “seams” under the rock
So coal is really very, very old wood; and that is why it burns so well. We may say that the flames of the burning coal are really sunbeams which the trees took in thousands of years ago when they grew in the forests.