TRANSITION ROCKS. ] 1 



istence. But, as has been well remarked, " Every island, 

 every continent, has formed part of an ancient bed of the 

 ocean, and this ancient bed is exposed to the examination 

 of thousands of observers in every degree of latitude not 

 covered by polar snows." Further, on finding this state- 

 ment in a work which proposes a classification of tertiary 

 strata, however ancient, by merely acquiring a knowledge of 

 the extinct and existing species contained in each, are there 

 not marks of inconsistency ? It is reckoned unsafe to judge 

 of the utter absence of highly organized animals, in very 

 old strata, by their not having as yet been found ; while the 

 fact of a tertiary system of strata containing a greater per- 

 centage of extinct shells than another, is considered as per- 

 fectly demonstrative of its greater age. We are not wishing 

 to inquire whether, in these instances, such a mode of exa- 

 mination will infallibly lead to a just conclusion or not ; but 

 it appears to be drawn as an inference from appearances pre- 

 cisely similar to those, which have induced geologists to be- 

 lieveinaprogression of development. As an argument against 

 the doctrine of progressive development, it has been affirmed 

 that the corals and mollusca, which lived in the ancient seas, 

 were not of a more simple structure than those which at pre- 

 sent exist. Those, however, who advocated the opinion that, 

 from the oldest fossiliferous deposit to the formations of our 

 own epoch, there were proofs, from examining fossil bodies, 

 that the standard of organization was gradually, and not 

 instantaneously, raised, never, either directly or indirectly 

 pronounced, as their opinion, that this " progressive de- 

 velopment" of organized beings was evinced by compar- 

 ing the members of any one genus, as they occurred in con- 

 secutive formations. It was never affirmed, as far as we 

 are aware, by any geologist, that, if a certain natural class 

 of organized fossil remains was observable in several forma- 



