FERNS IN STONE AND COAL 



many fern fossils are found, there must have been a 

 great number of those plants. Some of them were 

 very large, much larger than they grow now. 



It must have taken a long time for the coal to 

 become such a hard mass. It was certainly thousands 

 of years ago that these ferns grew. Let us see how 

 they changed, and why 

 the forms of these plants 

 can be so distinctly seen. 



Did you ever step 

 into soft, wet mud and 

 find that the shape of 

 your foot was left there? 

 That was because your 

 foot was harder than the 

 mud. This is what prob- 

 ably happened to the 



masses of plants. They formed at first a thick mat 

 of rushes, ferns, and trees. Then water flowed over 

 these beds, and mud, sand, and gravel settled there. 

 At length these formed thick layers on top of the 

 plants. They gradually pressed down close upon the 

 mass below, and there hardened into stone. The ferns 

 and other plants left their forms upon this rock wher- 

 ever they were pressed against it. Under this layer of 

 rock the plant mass, packed down, and kept warm, 

 but without light, gradually changed to coal. 



A Fern changed to Coal. 



59 



