layers were broken and folded in many curious ways. In valleys the rock layers rose more evenly. Just as soon as a point of rock rose above the water, rain and wind and frost and, after awhile, plants and animals began to wear it down. Slowly the valleys between the mountains were raised and filled with finely ground rock waste and leaf mold. The water from above gathered into lake bowls and river troughs.
You see the story of land goes around a circle. Mother earth is all the time tearing down and building up. She doesn't mind spending millions of years in grinding a mountain into mud and sand; pressing these into stone, and lifting the rock layers into mountain chains again. While she is about it, too, she puts gold, silver and copper, iron, lead and tin, salt, sulphur and coal, and many other things, into all the cracks and holes, and between the layers of stone. She hides diamonds and many precious jewels, too. It would take too long to tell here how she does all these things. It took men thousands and thousands of years to find the keys to unlock the prisons of all these useful and beautiful things.
You really ought to know about coal. It was made by pressure under sea water, like stones. But what do you think it was made of? Wood! Rocks may melt, but they harden again. Only plants will burn to ashes.
Ages and ages ago, simple plants like moss, with woody stems and no leaves, grew on big, quiet ponds until they covered the water. The moss died below, but did not decay, and it went on growing on top, until a spongy, floating mat many feet thick was formed. There are many such beds of moss today. They make a spongy brown fuel called peat. Peat is burned in Ireland and other countries. Peat would become coal, after a long time, if it sank below the sea, mud and sand or shells settled on it, and the sea water pressed it between layers of rock.
