44 



taining a few shells in a friable condition, extends to some depth be- 

 neath the level of the river, and appears to rest upon a bed of clay 

 of a lead colour, containing crystals of gypsum. At Evergreen a 

 stratum of pure white clay rests upon the upper layer of Eocene, 

 containing, embedded in its lower surface, large groups of crystals, 

 and seems to occupy the place of the black pebbles before mentioned. 

 The whole thickness of the Eocene deposite at this point appears to 

 be about twenty feet. Below as well as above this place, its height 

 declines until no portion of it is any longer visible above the water 

 edge. 



EOCENE DEPOSITE OP THE POTOMAC, RAPPAHANNOCK AND MATTAPONV, &C. 



Although the shores of these rivers have as yet been but little ex- 

 amined with a view to the structure and arrangement of the various 

 strata they exhibit, enough has been observed to prove that they are 

 no less rich in the Eocene marl than the other districts which have 

 been described. On Potomac creek, and for a great distance below 

 its mouth, the greensand strata may be seen running along the base 

 of the cliff; and from specimens examined, there can be no doubt 

 that the character of the deposite is similar to that of the Eocene of 

 the James river and Pamunkey. On the Rappahannock, for a con- 

 siderable distance below Port Royal, the very same appearance is 

 presented ; and the greensand obtained from some of these localities 

 is in every respect like that from the points already noticed. In some 

 places on the Mattapony, the occurrence of the greensand stratum 

 has been ascertained, while in others the beds containing this sub- 

 stance are replaced by beds of clay, which, though geologically of 

 the same (or Eocene) formation, are yet less likely to prove interest- 

 ing to the agriculture of the vicinity. Minute inquiries throughout 

 all this district, and throughout the corresponding region south of 

 the James river, are alone capable of developing the extent and va- 

 lue of this deposite. Even a great deal yet remains to be done in in- 

 vestigating localities on the James and Pamunkey rivers, the north- 

 ern shore of the latter being so far almost unexplored, and the pre- 

 cise character and value of some of the beds in localities examined 

 being but imperfectly ascertained. 



