GEOLOGICAL RELATIONS. Igg 



climate than the present, though they do not now exist 

 in southern latitudes, and therefore a very considerable 

 change in their habits must have since taken place. 

 Notwithstanding the facility with which the terrestrial 

 moUusks accommodate themselves to the physical influ- 

 ences which act upon them, such a change is not consist- 

 ent with what we know of their history, and hence the 

 most reasonable conclusion is, that the climate in which 

 they have lived, from the days when the multitudes 

 which now compose the mass of the fossil beds were in 

 the enjoyment of hfe upon the sm-face of the earth, to 

 the present time, has remained essentially the same. 



The question of the identity of this fossil, with any 

 living species of Helicina is also interesting, as upon its 

 solution, perhaps, may depend the opinion we may form 

 as to the comparative remoteness of the period when all 

 the fossil species of the formation flourished. If it 

 should be considered to be specifically distuict from any 

 other known living form, or in other words to be an ex- 

 tinct species, we should refer its existence to a more 

 ancient date in the tertiary period than would otherwise 

 be assigned to it. If on the other hand it should prove 

 to be identical with an existing species, it would date 

 back only to the most recent epoch. This point we 

 have established to our own satisfaction by carefully 

 comparmg specimens of the fossils of the Wabash de- 

 posit with the few specimens we have seen of the only 

 species of Helicina which inhabits the country north of 

 the tertiary section of the coast of the Gulf of Mexico, 



