366 CONTRIBUTIONS TO THE GEOLOGY OF 



the nature of the earthy materials, including the shells, or their casts, 

 as well as the conditions of the fossils themselves. Of the numerous 

 other localities which have been minutely explored, embracing almost 

 every exposure of the meiocene in the peninsula, it is therefore need- 

 less to give any description in this place. 



In the extensive area of flats already described as reaching from the 

 foot of the ridge of which Sprize Hill is the northern end, to the bay 

 shore, beds of marl have hitherto been disclosed only at a few points.- 

 On the land of W. Tomlin, Esq., near Kilmarnock, blue and yellow 

 marls have been found in several places, a few feet beneath the gene- 

 ral level of the flat, and it is particularly worthy of remark that the 

 fossils furnished by these shallow diggings are those usually found in 

 the meiocene of the neck, such as Ostrea compressirostra, Peciimculus 

 pulvinatiis and P.subovatus, Mactra motUcella, &c,, thus indicating the 

 prolongation of the meiocene strata to the very extremity of the pen- 

 insula. 



Of the Fossils of the Marl. 



The shells enclosed in these strata are usually in good preservation, 

 though generally so friable as readily to fall to pieces when spread 

 upon the ground. They are commonly found in groups or colonies, 

 and frequently throughout an extensive exposure only one or two spe- 

 cies can be met with. This is strikingly the case with the beds con- 

 taining Perna, of which a fine example is presented in the Stratford 

 clififs, as formerly described. It is perhaps still more remarkable of 

 certain strata of blue marl, found on the Potomac, at the point above 

 named; upon the Rappahannock in several places, and at some locali- 

 ties in the interior. This marl presents a beautiful aggregation of 

 very perfect small shells (Mactra modicella), bound together by a 

 rather tenacious blue clay, and rarely exhibits a specimen of any other 

 species. 



The shells most usually presented in the marl beds of the neck are 

 as follows: 



