240 COAL 



the trees in these forests lived and died, and the forests became 

 denser, and gloomier, and the masses of decaying vegetation 

 more and more impenetrable. 



In course of time, owing to changes taking place on the 

 surface of the earth, these forests were submerged ; the tossing 

 restless sea covered them, sand and mud fell upon them, and 

 the weight of the waters crushed them to death. 



Thousands of years passed by, and the forests had ceased 

 to be forests ; in their place had been produced a hard, shiny, 

 black mass, which we call coal. Yet in the coal we can still 

 find traces of these ancient trees, and can in imagination picture 

 the bygone forests of the carboniferous age. 



Nowadays, wandering over a desolate moor, or climbing 

 the steep sides of a lofty mountain, we may come upon little 

 mosses, which bear a most curious resemblance to the fossils 

 found in the coal-beds. 



One of these mosses is called Selaginella. It is a species 

 of club moss, and produces spores which contain resin. In 

 the coal-beds great fossil trunks, forty feet long, or more, 

 have been found, which are exactly like the trunks of the 

 selaginella, and spores, and other parts, too, have been 

 discovered which correspond to the spores of the selaginella. 

 These trees are called Lepidodendrons, from lepis, a scale, 

 and dendron, a tree. They are on the right-hand side in the 

 picture. 



In a similar way the little equisetum, or horsetail, of our 

 marshes, corresponds to the catamite of the coal forest ; 

 another very important tree was the Sigillaria, and besides 

 these there are fossil remains of many other great trees, and 

 ferns, and mosses. 



Still the centuries rolled by, and other changes occurred 

 in the earth's crust ; the sea receded, and the accumulations 

 of sand, pressed by the weight of the waters into sandstone, 

 became dry land ; plants again grew, and other forests were 

 formed, and so on during countless ages, until there came 

 a time when the surface and vegetation of the land were such 



