ancient distribution. 
117 
tween two and three hundred species have 
been detected in this formation, of which 
two thirds are ferns.”=^ * 
This catalogue exhibits but a short roll 
of family names, and yet it may be pre¬ 
sumed to include the bulk of the vegetation 
existing at the epoch when these materials 
were deposited. The results shew that the 
actual amount of vegetable life during the 
successive periods of this era, must have 
been enormous to our apprehensions, as com¬ 
pared even with the tangled forests of low 
tropical islands of the present earth. Mono¬ 
tony of form must then have obtained so as 
greatly to deprive the landscape of the 
charming variety of colour and outline, which 
now enriches and adorns the earth. 
Another and more important variation be¬ 
tween past and present is found in the 
extent of surface over which a particular 
race of plants is spread. 
The ferns, for instance, though some of 
the most widely scattered of existing plants, 
yet are not so widely distributed at present 
* Fossil Flora, 1. p. 10. 
