GROUPS OF PLANTS. 



69 



phytes. It is also called the Coal Age from the fact that the coal 

 measures were chiefly laid down during this period. ' By some it 

 is thought that the deposits of coal of this age were probably 



Fig. 45- A piece of slate from the coal formation in Shenandoah County, Pennsylvania, 

 showing a fossil fern which is probably a species of Neuropteris. 



principally formed from the remains of certain marsh plants 

 including two extinct groups of huge, tree-like club mosses 

 (Lepidodendron and Sigillaria) and the Calamites, representa- 

 tives of the scouring rushes. 



