Observations on the Eocene deposits of the United States. 



In a preceding No. of this work, (page 28) I alluded to a de- 

 posit of large oyster shells in South Carolina and Georgia, which 

 Mr Finch has termed Calcaire Ostree*, believing that it constitu- 

 ted a distinct formation, not referriable to*any particular period in 

 the scale of European deposits. I have since visited a portion of 

 the southern States, and can say, from personal observation, that 

 the continuous bed of oyster shells described by travellers and 

 others, includes, in fact, two distinct formations, one of seconda- 

 ry, the other of tertiary origin, and that two distinct species of 

 Ostrea have been confounded with that "finger post'" of the creta- 

 ceous strata, Exocjyra costata, Say.f These three shells combined 

 constitute that anomalous species called Ostrea gigantissima by 

 Mr Finch. Upon this supposed species was erected the formation 

 termed Calcaire Ostree, which we have proved to be no more than 

 the creation of Mr Finch's imagination ; yet a traveller ignorant 

 of the generic or specific character of the shells alluded to, would 

 be likely to arrive at the same conclusion with that geologist and 

 suppose that a continuous deposit, characterized by a single spe- 

 cies of Ostrea, extended from South Carolina to the Mississippi 

 river. Of the two species of Ostrea mentioned above, the (). sel- 

 hefonnis characterizes a peculiar stratum of the Eocene at Clai- 

 borne, and is also found in the newer cretaceous strata of South 

 Carolina. The O. Georgiana, (nobis) which much resembles O. 

 longirostris, Lam. is characteristic of the Eocene strata at Shell 

 Bluff on the Savannah river ; near Milledgeville, Georgia, and at 

 Orangeburgh, South Carolina. 



The Eocene first appears at Upper Marlborough and at Pis- 

 cataway, in Prince Georges county, Maryland. At the latter 

 place I observed it in 1830, and was the first to point out its rela- 

 tion to the London Clay, from inspection of its fossil shells. The 

 species are few in number, but the occurrence of the Cardita 



*Auierlca Journal of Science and Arts, vol. VII, p. 3. 



flu Dr. Goldfuss' splendid work, "Pctrifacten ", we observe the genus Exogyra 

 is credited to Sowcrby, whereas, our late and lamented naturalist, Thomas Say, Esq. 

 instituted it, and we consider it one of his happiest efforts in the subdivision of gen- 

 era, presenting us with an extremely interesting and natural group of shells peculiar 

 to the Cretaceous strata, which were previously referred to Chama by European 

 eonchologists. 



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