oy 34 



estuary but oceanic origin. M. Deshayes informs us that. 137 spe- 

 cies of Cerithium occur in the Paris basin, and this is said to be a 

 genus partial to estuaries. At Claiborne only three species occur ; 

 one is rare and a doubtful member of the genus, and of the other two 

 species I procured but one specimen of each, which tends to prove 

 that they were not in a situation favourable to their increase. The 

 stratum of oysters beneath -may have been deposited in a layoon, 

 but if so, the ocean must have returned and brought back the same 

 class of shells, which originated in the first bed of the Eocene sea, 

 whilst with this convulsion the Ostrea sellceformis entirely disap- 

 peared, and at the same time was deposited the debris of some rock 

 which then first mingled with the testacea ; and as this stratum of 

 sand and shells is only about fourteen feet thick, it was probably 

 soon formed, comparatively speaking, which will explain the 

 cause why so few species of testacea occur in comparison with syn- 

 t-hronous deposits in Europe. 



The following species of the Eocene at Paris occur also in the 

 sand at Claiborne: Solarium pat alum, (Lam.) S. canal iculatum, 

 (Lam.) ttulimus terebellatim, (Lam.) Siyaretus canal iculatus, 

 (Sow.) Calyptrtea trochiformis, (Lam.) Pyrula tricarinata, (Lam.) 

 Aricula triyona, (Lam.) Cytherea erycinoides, (Lam.) C. subery- 

 cinoides, (Desh.) Curbis lamellosa, (Lam.) Cardita planicosta, 

 (Blain.) Fistulana elonyata. (Desh.) 



8. A mass of Ostrea selUefonhis, about three feet in thickness, in 

 sand cemented by carbonate of lime. As this oyster also occurs in 

 the newer cretaceous strata, at first I supposed the present to be of 

 the same age as the latter deposit, but a subsequent examination of the' 

 inferior stratum convinced me to the contrary, as I found it charac- 

 terized by Eocene fossils exclusively. Large specimens of the Os- 

 trea generally have a water wojrn appearance, and occur mostly in 

 single valves ; the young which are vastly abundant are also disu- 

 nited, but invariably uninjured and unworn. Fragments of this 

 rock form a talus at the base of % the escarpment. 



4. A dark coloured marl, seventy feet in thickness, in which the 

 same Ostrea occurs, but smaller and less abundant than above. 

 Other fossils are very rare, but I found a specimen of Playiostoma 

 dnmosum, (Morton) which had attached itself while living to an oys- 

 ter shell, and this appears to be the only instance where the extinct 

 genus Ptagiostowa has been found in a tertiary deposit. 



5. The inferior stratum is an argillaceous, passing into calcareous 

 marl, containing the same species of shells that occur in the arena- 

 ceous deposit, but perhaps not so great a number of them ; the Car- 



[UOJ 



