THE SCENERY OF THE COAL PERIOD 157 



mites — were doubtless thirty feet in height. The impres- 

 sions of their huge and prostrate stems may often be traced 

 upon the shale which overlies a seam of coal. Of ferns, no 

 species living in temperate latitudes attains the dimensions 

 of a tree ; but there formerly flourished within the limits 

 of the Northern States ferns which attained to arboreal 

 dimensions, single fronds of which reached the length of 

 six to eight feet. The club-mosses — Lepidodendra — of the 

 same epoch grew to the magnitude and aspect of stately 

 palms (Fig. 66). Among us they trail upon the ground, 

 or rise but a few inches above it. The largest living club- 



Fig. 66. Remains of a Lepidodendron. 



