64 FOURTH KEPORT — 1S34. 



while strata strictly synchronous are forming, as great a dif- 

 ference may prevail between two groups of species inhabit- 

 ing remote sections of the same coast as is observable in 

 comparing those of our two secondary deposits. But on the 

 Atlantic coast of North America such differences should be less 

 than upon almost any other, from the influence of the gull- 

 stream, and other causes elsewhere stated. 



We are therefore at present at a loss to know how much of 

 this want of identity among the species we should ascribe to 

 disparity of age in the formations ; how much to difference in 

 the aqueous climate, and other circumstances controlling or- 

 ganic life. 



Until a more extended list of fossils shall have been collected 

 for the comparison, and, above all, until our geologists shall 

 have examined more in detail the phsenomena of the stratifi- 

 cation and structure of each region, I would recommend that 

 the question of their relative age be not anticipated by the ap- 

 plication of a common name, but that this point be left for a 

 season sub judice. 



I think it not improbable that we shall ultimately regard the 

 upper limestone of our superior secondary group in Alabama as 

 a somewhat newer formation than the inferior calcareous strata 

 of the same state on the arenaceous marl deposit of New Jersey. 

 The occurrence of several of its fossils among the fossils of the 

 overl}dng eocene seems to indicate that its true position is near 

 the top of the secondary series. 



Taken in their mineralogical relations, the marls and sands 

 of New Jersey would seem to occupy a place corresponding 

 nearest to the greensand formation of Europe ; and the lime- 

 stone strata of the south may be thought to harmonize imper- 

 fectly with the chalk, or a portion, perhaps, more truly with 

 the calcareous strata of Maestricht. Such certainly are their 

 rather obvious analogies mineralogicallj'^, but it is doubtful if 

 this ought to decide the question of their relative age. I would 

 not have it understood, therefore, that I view the American 

 upper secondary formations in any other light at present than 

 as the loose eqviivalents of the great cretaceous group of Europe. 

 I have already mentioned the existence of hut one, or at furthest 

 two species, to link the organic remains of these strata in the 

 two opposite continents. 



Another striking peculiarity, which also marks the want of 

 that resemblance which we might expect, is the absence from 

 these formations of any true chalk deposit. There would ap- 

 pear to be no sufficient evidence of the existence of this remark- 

 able formation in any known region of North America. May 



