492 PECULIAR MIOCENE MARL. 



bed has been found (by boring) on both sides of the Pamunkey 

 river, near to and in the same general range with the eocene bed, 

 and within a mile of two different excavations of eocene marl, or 

 gypseous earth, in different directions. Further, this Hampstead 

 niarl contains apparently as much green-sand as the neighbouring 

 eocene bed ; and there is no obvious difference in the texture, co- 

 lour, or general appearance of the two kinds. When I first visited 

 this locality (May, 1842), the digging had been suspended, and the 

 pits were full of water ; so that no marl or shells could be seen in 

 the bed. My examinations therefore were limited to heaps of the 

 marl which remained unspread upon the field. I was surprised to 

 find all of the few shells which met my eye in this imperfect view, 

 of species such as were unknown to me, and which I had not seen 

 in any other marl. But this did not induce me to suspect that 

 the formation was not eocene, as I was not then acquainted with 

 many eocene shells. Subsequently, however, by more full exami- 

 nation, and aided by the scientific knowledge of my friend M. 

 Tuoniey, Esq., whom I induced to visit with me this singular de- 

 posit, I learned that the shells, so far as recognised, were miocene ; 

 though mostly not known in any other of the miocene beds in Vir- 

 ginia of which, sundry exposures, with numerous different shells, 

 are within a few miles of the Hampstead bed. There are three 

 shells only, of some 22 species, which I found here, known to me 

 also in the other miocene marls of Virginia.* 



This bed is underlaid by the ordinary eocene of the neighbour- 

 hood. Suspecting this to be the fact in advance of any proof, I 

 procured an excavation to be sunk much lower than any had been 

 done before ; and, without any obvious change of general appearance 

 and texture, the eocene marl was reached as was made evident 

 by the finding of perfect shells of the ostrea sellceformis. 



From all the circumstances it would seem that the earthy mate- 

 rials of this miocene formation had been mainly derived from the 

 earlier formed and close adjacent eocene bed below, and which 

 spreads out to the westward ; and that while some flood had torn 

 up, swept along, and suspended for a time, and then deposited, this 

 fine green earth for the matrix, that the peculiar conditions permit- 

 ted the existence, with a few exceptions only, of shell-fish not belong- 

 ing to the ordinary miocene. The supposed position of this peculiar 

 miocene is represented (at 9) in the annexed profile of all the 

 strata. 



This peculiar deposit, and this alone so far as known to me, would 

 accord with the cases asserted by Professor Rogers, of the frequent 

 and general occurrence of green-sand in large proportions, in ordi- 

 nary miocene marls. But even this case afforded no support to his 



* There three are cardita granulata, an astarte, and one other. 



