30 



an oyster^ shell, and this appears to be the only instance where 

 the extinct genus Plagiostoma has been found in a tertiary de- 

 posit. 



5. The inferior stratum is a dark colored clay, passing into 

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

 naceous deposit, but perhaps not so great a number of them ; the 

 Cardita planicosta is in great abundance, but does not attain to 

 one half the size of specimens common in the sand. 



The insulated position of the Eocene at Claiborne, is remarka- 

 ble ; west of the vicinity of the village, the whole country is se- 

 condary, or of that limestone which Dr. Morton has compared to 

 the Maestricht deposit, and termed the " newer cretaceous strata". 

 As we proceed west, we traverse hills of the same limestone but 

 find no trace of the tertiary until we arrive at St. Stephens, on 

 the Tombeckbe, where it is still more isolated than at Claiborne, 

 being bounded immediately from the river by the cretaceous stra- 

 ta on the west, and on the south by alluvium which intervenes 

 between it and the secondary. On the north it also dips under 

 the alluvium, and appears to be the rock which forms the rapid 

 two miles north of St. Stephens, the first which is met with in 

 ascending the river. The tide flows to the foot of this rapid, a 

 distance of ninety miles from the head of Mobile Bay, but this 

 happens only in the lowest stage of the water. 



From some notices which have been published respecting the 

 elevated bluff at Natchez, on the Mississippi, we infer that is of 

 the formation in question, which, crossing the river, reappears on 

 the banks of the Washita, near the town of Monroe, in Louisiana, 

 where it is associated with cretaceous strata. This locality is of 

 great interest to a geologist, as it will, when investigated, solve 

 a problem of great importance, whether or not remains of the 

 Saurian family exist in the tertiary. The gigantic vertebrae of 

 the BasilosauraSy (Harlan) were found here enveloped in Eocene 

 marl, but remains apparently of the same speries, from the new- 

 est secondary limestone of Clarke county, Alabama, have been 

 sent to this city by John G. Creagh, Esq. and by A. B. Cooper, Esq. 

 of Claiborne. These highly interesting remains were found on 

 the plantation of Mr Creagh, and are now in the possession of 

 Dr. Morton, who has laboured diligently to procure whatever 

 may advance a knowledge of American geology. 



In Wilcox county, Alabama, on the plantation of my friend 

 Judge Tait, the Eocene appears in the form of a dark colored 

 Randstono, iii which the shells are only traced by imperfect chalky 



