360 CONTRIBUTIONS TO THE GEOLOGY OF 



Among the various substances found in the strata of these cliffs, 

 especially towards the lower extremity, are to be enumerated distinct 

 and beautifully compact lignite and fibrous carbonate of lime. The 

 latter is found in the interstices of a yellowish clay, forming the stra- 

 tum next beneath the diluvium, and is sometimes in sufficient quantity 

 to render the clay quite calcareous. 



An average specimen of the blue marl, from the lower of the two 

 strata just described, yielded in the one hundred grains forty-four and 

 three-tenths grains of carbonate of lime ; from the upper only twenty- 

 one grains. 



The Chantilly cliffs, situated below the mouth of the creek of the 

 same name, adjoining the ancient residence of Richard Henry Lee, 

 and about two miles further down the river than those of Stratford, 

 may be regarded as a continuation of the former, having the same 

 average elevation, and being composed of very similar materials. At 

 this point, however, the fossiliferous stratum has much greater thick- 

 ness, sometimes reaching from the water's edge to a height of nearly 

 twenty-five feet. A less proportion of the Perna is presented in this 

 bed, which principally consists of Madras, and other small bivalves, 

 together with several species of Pedens. The beach is strewed with 

 fragments of ferruginous sandstone, which have fallen from the upper 

 portion of the cliff, where a band of this material overlies the shelly 

 strata of the meiocene. These masses exhibit the impressions of 

 Tedens and other shells, beautifully clear and sharp. 



An interesting illustration of the fertilizing properties of some of the 

 materials composing the Stratford and Chantilly cliffs is deserving of 

 mention in this place. Zones of vegetation, consisting of clover, toge- 

 ther with scattered locust trees, may be observed at the proper season 

 extending to a great distance along the face of the cliffs, marking dis- 

 tinctly the limits of the marl or gypseous clay, and rarely encroaching 

 upon the other strata. Even where the surface is almost vertical, this 

 beautiful drapery is retained. 



Bank of the Potomac, below the Mouth of Lower Machodoc River, in Westmoreland County. 



At Cole's Point, situated on the south side of the mouth of the 

 Lower Machodoc, commences a low bank, which is prolonged for 



