278 



MIOCENE STRATA OF VIRGINIA. 



[On. XV. 



they can be truly said to be the representatives of these two European 

 formations, they may range in age from the Older Pliocene to the 

 Miocene epoch, according to the classification of European strata 

 adopted in this chapter. 



The proportion of fossil shells agreeing with recent, out of 147 

 species collected by me, amounted to about 17 per cent., or one-sixth 

 of the whole ; but as the fossils so assimilated were almost always the 

 same as species now living in the neighboring Atlantic, the number 

 may hereafter be augmented, when the recent fauna of that ocean is 

 better known. In different localities, also, the proportion of recent 

 species varied considerably. 



On the banks of the James River, in Virginia, about twenty miles 

 below Richmond, in a cliff about 30 feet high, I observed yellow and 

 white sands overlying an Eocene marl, just as the yellow sands of the 

 crag lie on the blue London clay in Suffolk and Essex in England. In 

 the Virginian sands, we find a profusion of an Astarte (A. undulata, 

 Conrad), which resembles closely, and may possibly be a variety of, 

 one of the commonest fossils of the Suffolk Crag (A. bipartita) ; the 

 other shells also, of the genera Natica, Fissurella, Artemis, Lucvna, 



Fig. 20T. 



Fig. 208. 



Fulgur canaliculatus. Maryland. 



Fusus quadricostatus, Say. Maryland. 



Chama, Pectunculus, and Pecten, are analogous to shells both of the 

 English crag and French faluns, although the species are almost all 

 distinct. Out of 147 of these American fossils I could* only find 13 

 species common to Eurbpe, and these occur partly in the Suffolk 

 Crag, and partly in the faluns of Touraine ; but it is an important 

 characteristic of the American group, that it not only contains many 

 peculiar extinct forms, such as Fusus quadricostatus, Say (see fig. 

 208), and Venus tridacnoides, abundant in these same formations, but 

 also some shells which, like Fulgur carica of Say and F. canaliculatus 

 (see fig. 207), Calyptrcea costata, Venus mercenaria, Lam., Modiola 

 olandula, Totten, and Pecten magellanicus, Lam., are recent species, 

 yet of forms now confined to the western side of the Atlantic — a fact 

 implying that some traces of the beginning of the present geographi- 



