328 



Overlay. 



PAMUNKEY MARL. 



FlGITRE 1. 



Sandy surface soil, about 6 inches 



Sandy sub-soil, dry and firm "> 

 Loose and dry sandy gravel / 



Indurated ferruginous sandy \ 

 gravel, wet, 1 foot } 



Feet. 



Wet and adhesive green clay, ("olive earth") 1 foot 



Marl. 



Soft and pervious clay marl, 6 inches 

 Compact and impervious clay marl, 5 feet 



Softer layer, 1 foot 



Layer of stony lumps, 1 foot 



Gypseous, or green-sand earth, with very little shelly mat- \ 

 ter, of great and unknown thickness at least 40 feet j 



The soil of the overlying land is a rich black sandy loam (before 

 drained and cultivated), 6 or 8 inches deep, lying on a sandy 

 subsoil, firm and dry, and becoming more coarse and loose as de- 

 scending, until it is more of fine gravel than sand. All the above 

 layers, varying from 2 to 4 feet in the successive uncoverings, are 

 dry and easy to dig and remove. Below these, the gravelly sand 

 is more or less cemented into a hard and almost stony bed, by the 

 percolation of ferruginous spring water. Under this layer, which 

 is full of veins of springs, coming from beneath the higher ground, 

 there lies a very uniform layer, from 8 to 14 inches thick, of green 

 clay, which is the water-bearing stratum, and keeps the lower part 

 of the gravel above full of water. This green clay has a very pe- 

 culiar appearance and texture. Though very largely constituted 

 of pure clay, and extremely adhesive and close after being moved, 

 yet in its bed it is very soft and pervious to slowly-oozing water, 

 and, of course, is saturated by the numerous veins of springs above. 

 I think that this green clay was formerly the. upper part of the 

 marl ; and has had all its former shelly matter decomposed and 

 carried off by the constant access and passage of water containing 

 salts of iron. The upper 4 to 6 inches of the marl immediately 

 below this clay, seems as if in transition to the same state. It is 

 soft, permeable by water, miry, and adhesive, all which are qualities 

 of the clay above, and entirely different from the compact marl 



