21 



centenaria, &c. This stratum, varying from three to four feet in 

 thickness, is a mass of compacted shells, with but little earthy- 

 matter intervening. The earthy matter contains a very large pro- 

 portion of the chloritic sand. The next stratum is composed chiefly 

 of large Pectens, and has a thickness of from one to two feet. Be- 

 low this is another dense stratum of Chama, together with Area 

 centenaria, Panopea reflexa, &c, and also very rich in the green 

 sand. Thickness, from four to six feet. Then follows a second 

 layer containing Pectens with Ostrea compressirostra, one foot in 

 thickness. A third stratum in which Chama predominates, follows 

 next, in thickness from two to three feet, and at the base of the 

 cliff is a layer containing Pectens, Ostrea compressirostra, &c. from 

 four to five feet in thickness. 



Thus through a height of more than twenty feet in some places, 

 the cliff consists principally of shells, of which there are a great 

 many species, besides those mentioned as predominating in the 

 several beds. On the extensive contiguous estates of King's mill 

 and Littletown, these shells are largely used as a manure : and for 

 this purpose the first and second beds of Chama are preferred on 

 account of the immense amount of calcareous matter, and the large 

 proportion of green sand which they contain. Judging from the 

 occasional appearance of bluish green clay on the line of the beach, 

 and in some places immediately at the base of the cliff just de- 

 scribed, it is highly probable that a continuous stratum of this sub- 

 stance lies beneath the other beds throughout the whole extent 

 observed. A horizontal bed of yellowish clay extends for some 

 distance along a lower portion of the cliff, in which there are no 

 fossils ; running within a few feet of its upper edge, and beneath 

 this bed, and parallel to it, is a thin layer of the iron ore formerly 

 described. At the foot of this cliff appears the underlying stratum 

 of clay. 



DESCRIPTION OP THE CLIFFS AT Y0RKT0WN ON YORK RIVER. 



The elevation, abrupt form, and peculiar construction of the cliffs 

 at this point, and for some distance, both above and below, render 

 it an interesting spot to the geologist. A dry and ample beach, un- 

 interrupted by creeks or inlets for several miles, affords a ready 

 access to the banks, while the river's edge, strewed with fossils 

 which have fallen from the cliff, exposes a considerable variety of 



