58 



classes. That division into two classes is there- 

 fore natural. 



The characters of the transition class, as they 

 have been laid down by those who have adopted 

 it, are, the presence of organic remains, or the 

 occurrence of fragments of previous rocks in the 

 composition of its strata; implying an origin 

 partly mechanical. It is further necessary, ac- 

 cording to the hypothesis, that the rocks of this 

 character should occur in a position intermediate 

 between the secondary and primary rocks ; thus 

 forming, according to the view of its founder, a 

 transition between the secondary strata, of which 

 the origin and structure are supposed to be me- 

 chanical, and the primary, esteemed to be purely 

 chemical. It is therefore obvious, from the na- 

 ture and consequences of geological alternation, 

 that wherever a stratum of the transition class is 

 found, all those strata which lie between it and 

 the secondary class, must also appertain to the 

 former. 



In examining the value of these characters, it 



