REPORT ON THE GEOLOGY OF NORTH AMERICA. 45 



creek. The ridge dividing the waters of the Alabama and Tom- 

 beckbe, also secondary, is composed of cretaceous limestone, full 

 of Nummulites Mantelli (Morton). St. Stephens, on the 

 Tombeckbe, is situated on a bluff of the same, about one hundred 

 feet in height ; but the eocene appears a short distance north of 

 it, separated from the secondary by a strip of alluvial soil. Here, 

 however, the two upper strata only are visible, the superior bed 

 of limestone being but a few feet in thickness, whilst at Clai- 

 borne the corresponding one is about forty-five feet thick. The 

 arenaceous stratum is precisely similar to that of Claiborne, but 

 the fossils are not so well preserved, and are chalky and friable. 

 We know of no locality west of this, in Alabama or Mississippi, 

 where the eocene formation occurs ; but on the Washita river, 

 near the town of Monroe, it is associated with the strata of the 

 cretaceous group, as Mr. Conrad ascertained by examination of 

 some fossils sent to the American Philosophical Society by Judge 

 Bry. The most abundant fossil beds of the eocene at this place 

 appears to be Corbula oniscus (Conrad), a shell very common 

 in the arenaceous strata at Claiborne. 



No other information has been received of any other localities 

 of eocene deposits, but doubtless many will be discovered when 

 geology is pursued in a more systematic manner. 



The following diagram will explain the order of succession 

 and the thickness of the strata in Claiborne Bluff, and to these 

 are added the two members of the cretaceous group, which oc- 

 cur in the vicinity. Those species are indicated which occur in 

 both formations ; they are highly interesting, as they furnish in- 

 dubitable evidence of the antiquity of these tertiary beds. Among 

 more than two himdred species of shells at Claiborne, there is 

 not one which is identical with a fossil of the pleiocene of this 

 county ; one only is even an analogue : not one can be referred 

 to any recent species, much less to a native of the coast of the 

 United States. One only, Lutraria papyrea (Conrad), is the 

 analogue to a species of our coast, L. canaliculata (Say), in its 

 general appearance, but is very remarkable in having the um- 

 bones turned in an opposite direction to those of the latter spe- 



