REPORT ON THE GEOLOGY OF NORTH AMERICA. 43 



cent on our coast. It is evident that here the proportion of 

 living species is greater than in most of the preceding localities, 

 the proportion being something like 22 per cent. Should this 

 ratio not materially vary with new discoveries, the deposit must 

 be ranked, like the preceding, with the meiocene period, notwith- 

 standing that its shells are rather the analogues of the European 

 older pleiocene. 



York, Virginia. — About forty-four species are known from 

 this spot, thirty-six of which are extinct, and the remainder 

 recent. The living species here are nearly 18 per cent, of the 

 whole, which differs but little from the ratio at Suffolk. 



Smithfield, on the James River, Virginia. — The deposit at 

 this place has furnished sixty-four species, fifty-five extinct and 

 nine recent. This affords a proportion of about 14 per cent., 

 which, if it be taken as the true expression of the relations of 

 the species, would place the locality in the meiocene, and per- 

 haps in an older division of the period than would belong to some 

 of the preceding deposits. 



North Carolina. — Though the fossil shells of this State have 

 been very little examined, the present list indicates a group of 

 beds decidedly more modern than any detailed above. Of thirty- 

 seven species at present known, twenty-four, or nearly two 

 thirds, are recent : should this proportion remain nearly the 

 same, after the catalogue has been duly augmented, we must 

 rank some at least of the interesting deposits of North Carolina 

 in our older pleiocene, placing them most probably late in the 

 period. A certain modern aspect about these shells lends coun- 

 tenance to this prediction. 



I shall terminate this account of our middle tertiary beds with 

 a list of the fossil shells of this period, which are common to 

 the strata of both America and Europe. They are: 



1. Liicina divaricata, Lam. 



2. Cerithium melanioideum, Sow. (In the London clay.) 



3. Ostrea Virginian a, Gmel. 



4. Dentalium dentalis, Linn. (D. alternatum, Say.) 



5. Venus rustica ? Sow. (Isocardia fraterna, 5a«/.) 



6. Pectunculus subovatus. Say. (P. variabilis, Sow.) 



Older Tertiary, or Eocene. — The first notice of eocene de- 

 posits occurring in the United States, as characterized by organic 

 remains, was published by Mr. Conrad in the Journal of the 

 Academy of Natural Sciences in 1830, from observations he had 

 made in the vicinity of Fort Washington, in Maryland : he also 

 stated that such beds occurred at Vances Ferry, on the Santee 

 river, where it is since ascertained that they are covered by a su- 

 perficial deposit of the fossils of the pleiocene period. One cha- 

 racteristic fossil of the eocene of Claiborne {Ostrea sellceformis, 



