REPORT ON THE GEOLOGY OF NORTH AMERICA. 41 



the Eutaw springs, which is wholly secondary. The deposit 

 therefore at Vances Ferry is probably very limited in extent, 

 and extremely superficial, capping the cretaceous rocks in the 

 same manner as at Wilmington. 



" The pleiocene probably occurs on the Santee river, near the 

 junction of the Congaree and Wateree rivers, as Mr. Say de- 

 scribes two species of Area, evidently pleiocene fossils, from a 

 locality near the junction of these two rivers." 



Such, then, are the principal localities at present known of the 

 middle tertiary formations in their apparently continuous range 

 from the Delaware to the Santee, over a tract perhaps eighty 

 miles in breadth from the coast. In external character, mineral 

 contents, and organic remains, the sedimentary deposits over 

 this great tract exhibit a most marked uniformity, and were it 

 not that the principle has been furnished us whereby, through 

 a comparison of recent and extinct fossils, the relative antiquity 

 of each locality may be determined, at least approximately, we 

 should, vrithout a doubt, regard the whole tract as one simul- 

 taneous formation. I look confidently, however, for both older 

 pleiocene and meiocene proportions among the species, and shall 

 not be surprised if we discover, ultimately, almost every inter- 

 mediate ratio. For this intimate association of the two periods 

 there would seem to exist a natural and obvious cause. The 

 whole of our tertiary, and even cretaceous groups, are all de- 

 posits effected under the same general physical exposures, all 

 accumulations upon the same coast, bearing traces of no con- 

 vulsions, and therefore interrupted by no hiatus. These for- 

 mations occupy one extensive plain, where the stratification is 

 amazingly horizontal, which is crossed by no ridges, and there- 

 fore subdivided into no basins ; so that the whole may be con- 

 sidered as having resulted from a set of causes continuing in ac- 

 tivity throughout a long period. 



Having procured a table of all our middle tertiary fossils at 

 present known to us, and with it an enumeration of the species, 

 recent and extinct, from the more important localities which 

 have been explored, I am enabled to attempt a determination of 

 the relative age of these beds, from the numerical relations of 

 the shells. 



The total number of species from our tertiary beds, excluding 

 the eocene and the newer pleiocene, is about 195 ; of these, nearly 

 forty are known as recent shells, inhabiting principally our own 

 coast. This presents us with a proportion of rather more than 

 twenty-one in one hvmdred, or about the ratio of the living spe- 

 cies in the meiocene formations of Europe. 



From New Jersey to North Carolina there is every reason to 



