356 CONTRIBUTIONS TO THE GEOLOGY OF 



not immediately in the line of the violent action of the diluvial vs^ave 

 or current, the incumbent beds of marl remain in place. 



Moreover, there is reason to believe that the sandstone is spread out 

 towards the east, below the eocene strata, and that its depth alone con- 

 ceals it generally from the view. Where, therefore, in consequence of 

 some local irregularity of its surface, it was less deeply buried, w'e 

 might naturally expect, even at some distance within the confines of 

 the eocene, to see its upper stratum exposed to day. Accordingly, at 

 some points a good deal eastward of the line of boundary, we meet 

 with very distinct exposures of this rock. Of this a good example is 

 presented at Gray's mill, on Muddy creek, near the Rappahannock, 

 where, in a ravine by the road side, may be seen the blue and ferru- 

 ginous material of the marl, while upon the other side of the road is a 

 ledge of coarse, soft and whitish sandstone, over which the mill-stream 

 flows. 



Arrangement and Composition of the Meiocene Strata of the Peninsula, 



The strata composing the meiocene, in this portion of the state, are 

 in general analogous, in arrangement and materials, to those of the 

 same formation in the peninsula of the York and James rivers, as de- 

 scribed in our former communication. 



The two interesting general facts of the occurrence of the bluish 

 marls low down in the series, and the presence of a thin band of ferru- 

 ginous rock or clay on the top of the marl, and between it and the di- 

 luvial strata, are not less distinctly observable here than in the region 

 formerly referred to. Indeed, so uniform is this position of the band 

 of iron rock, in regard to the beds of marl, that the discovery of this 

 material, at any point, would furnish strong grounds for believing that 

 the fossiliferous strata existed at some depth beneath. 



In general, the blue marl is observed to be the richest in fossils, and 

 is hence found most available in agriculture. In many places, how- 

 ever, especially towards the eastern termination of the peninsula, the 

 shells occur in sand and clay of various shades of yellow and brown, in 

 sufficient proportions to form highly valuable marls. 



The fragmentary rock, consisting of broken shells, cemented by car- 

 bonate of lime, sometimes partially crystallized, and the white, pulve- 



