40 



THK GEOLOGICAL HISTORY OF PLANTS. 



[ shales and limestones of the Silurian owe their, carbona- 



I ceous matters to the decomposition of Algse, though pos- 



1 sibly some of it may have been deriTed from Graptolites 



and other corneous Zoophytes. In any case, such micro- 



Fio. li. — Silurian vegetation restored. I^otannularia.^ Berwynia, Nema- 

 tophyton, Sphenophyllum^ AHlirosHgma, Fnlophyton. 



Ecopic examinations of these shales as I have made, have 

 not produced any evidence of the existence of plants of 

 higher grade, while those of the Erian and Carboniferous 

 periods, similar to the naked eye, abound in such evi- 

 dence. It is also to be observed that, on the surfaces of « 



