358 CONTRIBUTIONS TO THE GEOLOGY OF 



the interior casts of the fossils, formed of the general substance of the 

 bed, may often be extracted in great numbers in a perfect condition. 



In the blue marl, as well as other strata containing fossils, in the neck, 

 there is often present a notable proportion of green sand, and at some 

 localities of the meiocene this material is found mingled pretty largely 

 with common sand and clay, in strata in which no fossils can be found. 



Besides the overlying band of ferruginous rock before described, 

 there occurs, in some places in the neck, another similar stratum, nearly 

 on the top of the diluvium. This, of course, presents no marks of 

 organic remains, and is generally but an aggregation of coarse gravel 

 and sand, cemented by ferruginous matter. 



Description of some of the more interesting Localities in the Meiocene 



District of the Peninsula. 



To give clearer conceptions of the arrangement and character of the 

 strata, of which a general sketch has just been presented, a detailed 

 account of them, as exhibited at several of the more important locali- 

 ties in the Neck, will now be introduced. Details of this description, 

 whilst they furnish the scientific inquirer at a distance with that pre- 

 cise information in regard to the geological structure of the region 

 which he is chiefly interested to obtain, are not unattended with ad- 

 vantages of a more practical kind, by affording to all who are directly 

 interested in the resources of a district, an easy mean of examining 

 them for themselves. 



Stratford and Chantilly Cliff's. 



These noted cliffs, situated in Westmoreland county, extend along 

 the Potomac for several miles, on both sides of the mouth of Chantilly 

 creek, rising, in some places, to an elevation of about one hundred feet, 

 and in others subsiding to lower levels, or sinking, for a short space, 

 into the ordinary river flats. At a point a little above the mouth of 

 the creek, what are properly termed the Stratford cliffs begin. Thence 

 they continue up the Potomac, with but little interruption, for about 

 four miles. For some distance from their lower termination, they 

 present the following order of strata. 



1. At the base, and extending to the height of from fifty to seventy 



