202 PECULIARITIES OF THE FOSSILS. 



and of Neritina, not present in the other two, 

 and in the two lower horizons, there are two 

 species of Melanopsis peculiar to each. 



So very different are the several fossils of one 

 zone from those of another, that at first examina- 

 tion, we appear to have before us very distinct 

 and well marked species, and that each series 

 of horizons was characterised by Paludmce, Neri- 

 tince, and Melanopsides, peculiar to itself, and 

 representative of those inhabiting the other 

 divisions. This would be a very startling phe- 

 nomenon to occur within so limited an area. If 

 the successive species be considered distinct, 

 we must regard them as mutually representative, 

 and hold that a succession of creations and 

 extinctions took place, in this probably limited 

 basin, during a brief geological period, — or else 

 that a transmutation of species took place. 



A careful study of the forms in question, and 

 an inquiry into the modes and capacity of varia- 

 tion of species in the genera to which they 

 belong, and among their allies, have convinced 

 us, however, that these curious changes of form 

 may be accounted for otherwise, and that in the 

 successive Paludince, Neritince, &c. we have 

 before us only the same species assuming pro- 



