362 CONTRIBUTIONS TO THE GEOLOGY OF 



and sulphate of alumina effloresce upon the surface, and sulphur is dis- 

 tinctly indicated. 



Irregular nodules of ferruginous clay are found imbedded in the 

 other materials, presenting the curious feature of a crystalline nucleus, 

 consisting of pure selenite. In some portions of the cliff these crystals 

 are of considerable size, arranged in their usual starlike form, and so 

 abundant as to suggest the utility of employing these clays in the agri- 

 culture of the neighbouring parts of the neck. An average specimen, 

 taken from a part of the cliff where a similar material was quite abun- 

 dant, afforded by analysis, in the one hundred grains, ten grains of 

 sulphate of lime. 



Banks of the Rappahannock above the Month of Curratoman River, Lancaster County. 



In proceeding down the river from the neighbourhood of Belmont, 

 the residence of Dr Jones, about eight miles above the mouth of Cur- 

 ratoman, the cliffs, for some distance, present heavy beds of clay and 

 sand, overlaid by the ordinary diluvium, and resting upon a stratum of 

 soft ferruginous sandstone, graduating into a sandy clay, and sometimes 

 a yellowish sand, mottled with ferruginous spots. Following these 

 strata for a distance of one and a half miles, we meet with a rocky 

 layer, consisting entirely of shells, converted into brown oxide of iron, 

 situated at the base of the cliff. This continues in the same direction 

 for a distance of one and a quarter miles. The following is the order 

 of the strata composing the bank at a point near its eastern termination : 



1. Beneath the base of the cliff, as it is exposed, and also underly- 

 ing the beach sand, is a blue marl, containing numerous shells, and 

 having a sensible amount of green sand. These shells are chiefly the 

 Perna, different species of Venus, Natica and Oliva, 



2. Running along the base of the bank, the ferruginated, shelly 

 rock above described, four feet in thickness, and containing the same 

 fossils as the stratum beneath. 



3. Five feet of sand, with ferruginous blotches and streaks. 



4. Six feet of diluvium. 



Below this, and within a short distance of the Curratoman, marl 

 beds occur below the level of the flats, consisting chiefly of a peculiar 



