1852.] 193 



As the deposit is a, conglomerate and in the vicinity of cretaceous beds, it 

 would occur to any one that the presence of a few cretaceous forms could be 

 easily explained by supposing the breaking up of a cretaceous bed, and the 

 transportation of its debris and included fossils into the eocene sea, where they 

 were entombed with the molluscous remains of that period. Nevertheless it is 

 evident that the cretaceous shells were filled at the eame time, and with the 

 same mineral matter as those of the eocene found with them, for the casts of 

 both are composed of compact white limestone. Now, excepting the stratum 

 on Timber Creek, New Jersey, none of our cretaceous deposits could furnish 

 the mineral matter of either the casts of these shells or the rock in which they 

 are enclosed. Between the Delaware and Chattahoochee the cretaceous rocks 

 are made up of loose, grey, loamy and silicious strata, without white creta- 

 ceous beds ; and in Alabama, the rotten limestone, which is the prevailing rock, 

 is entirely different from the Wilmington bed ; even the cretaceous deposit in 

 the vicinity, from which it might be supposed these remains were derived, is 

 composed of the usual dark-colored silicious stratum of green sand. It would 

 be equally difficult to account for the presence of these fossils, by supposing 

 that they remained empty and were subsequently drifted into the eocene sea, 

 and there filled with sedimentary matter and buried with the forms of that 

 period. At all events, after a careful examination of the locality, as well as 

 the fossils, I could satisfy myself only by supposing the inhabitants of these 

 shells to have lived and died during the eocene period, to have been cotempora- 

 neous with the forms with the remains of which they are buried. 



The fossils to be described are for the most part in the form of casts : fre- 

 quently, however, casts of both the interior and exterior of the shells occur, 

 and they are generally so characteristic that there can be but little danger of 

 mistake, if even hereafter the shells themselves should be found. 



1. Trochus nixus : large ; axis very oblique ; whorls 5 or 6, flat or slightly 

 concave, marked by revolving lines obsoletely cancellated ; suture of the cast 

 deep, of the shell basely impressed ; umbilicus open, deep. 



JDimen. Spiral angle 75 j hr. 4; br. 5 in. 



2. Pyrula ampla : ventricose, ovate ; epire depressed ; whorls 4, last one 

 very large. 



Dimen. Spiral angle 100 ; ht. 6in. ; br. 4-5 in. 



This fossil is also found in the white limestone of the Santee. 



4. Fdsus abruptus : ovoid ; whorls rounded, ventricose, the last one termi- 

 nating abruptly in the canal. 



Dimen. Spiral angle 70 ; ht. 6 in. ; br. 4 in. 



4. CoNus MUTiLATUS : Spire depressed ; whorls flattened ; sides longitudinally 

 convex. 



Dimen. Spiral angle 101; ht. 2-5 in. ; br. 1-5 in. 



Casts of shell are abundant at Wilmington, N. C, and in the white limestone 

 of Alabama. It is also found in the eocene beds on the Santee. TLey are 

 easily distinguished from the other eocene species. In C. gyratus^ Morton, the 

 spire is more produced ; whilst in C. i?auridens^ Don., it is more depressed. 

 Casts of the latter have the spiral whorls in nearly the same plane. 



5. VoLUTA coNoiDEs: conical ; spire short; whorls 4, columcllar plaits nu- 

 merous. Resembles Conus gyratus. 



Dimen. Spiral angle 87; ht. 2 in. ; br. 1 in. 



6. Trigonia divaricata: cast of left valve, ribs 15, somewhat acute, con- 

 verging towards the posterior margin, arched on the umbones, diraricating be- 

 low. After the sixth rib there is a half rib intercalated. 



Dimen. Length 2 in.; br. 1*5 in. ; ht. 1 in. 



7. T. LCNATA : ribs 14, rounded, slightly ventricose; posterior margin cre- 

 nulated. 



Dimen. Length 1-75 in. ; br. 125 in. ; ht. 1 25 in. 



