172 PROCEEDINGS OF 



the level of the sea ; and, therefore, the only cause which presents itself to the mind 

 of the inquirer is, a fall of temperature in the ocean, sufficient, at the close of the 

 lower tertiary period, to have destroyed every kind of animal life, at least on the 

 coast of North-America, because of two hundred species of tiie lower tertiary, not 

 one exists on the coast, nor is found in the more recent formations of the Union. 



The lower tertiary is certainly identical with the London clay and calcaire 

 grossiere, or eocene formation ; and I was led to the comparison, in the first place, 

 by discovering the Cardita planicosta, a well-known characteristic fossil of the eo- 

 cene period in Europe.* A single species of shell will thus occasionally indicate 

 the stratagraphical relations of a formation hitherto obscure or unknown, and lead 

 to inferences the most important, which he who underrates organic remains is apt 

 to regard as visionarj', but the palfDontologist must acknowledge as useful and true. 



At Upper Marlborough, Prince George's county, Maryland, and at other locali- 

 ties in Maryland and Virginia, groen-sand, the same in mineral character with that 

 of the cretaceous period, enters largely into the composition of the lower tertiary 

 marls. In Georgia, and more rarely in Alabama, a portion of this formation as. 

 Bumes the character of burr stone, and the shells which abound in it are beautifully 

 silicified. Near Piscataway and Upper Marlborough, the lower tertiary is some- 

 what similar, in general appearance, to the Bognor rocks of Great Britain, but of a 

 coarser and more arenaceous texture. What is of more consequence, however, is 

 the occurrence of a bivalve shell, characteristic of the Bognor rocks and of the 

 eocene period — Ostrca bellovacina. This stratum is indurated, and overlies the 

 eocene green-sand, but is evidently linked with it by a communion of zoological cha- 

 racters, at the same time that it contains a few species which appear to bo peculiar 

 to it. Panoptza elongaia is the most abundant fossil, and a new Pholas, (P. Petro- 

 sa,) and a Pholadomya, (P. Marylandica,) I have met^with only in this rock. Sev- 

 eral other shells, which it holds, arc identical with species of the lower tertiary at 

 Claiborne, Alabama. The most interesting shell is Gryphaja vomer, {Oslrea late- 

 ralis, Nillson,) which originated in the lower division of the cretaceous system, 

 was continued in the two upper terms, and reappears in the tertiary sandstone at 

 Upper Marlborough iu abundance, although no other fossil whatever, of the creta- 

 ceous group, has been found in that locality. 



In company with my friend Francis Markoe, Jr., of Washington, I reexamined 

 the interesting deposits at Upper Marlborough, and was surprised to find the 

 secondary species of Gryphiea scattered in abundance over the surface of the disin- 

 tegrating rock, in company with tho characteristic group of the eocene ; for, on a 

 former visit to this place, the shell was so rare that I supposed it to be accidental, 

 or part of the ruins of an earlier era. The valves were never found united; but 

 this is seldom the case in the New-Jersey green-sand deposits, where it is nume- 

 rous. Although the lower valve is always more or less broken, the fracture has re- 

 sulted from the fragility of tho shell, in falling, through the agency of frost and rain, 

 from the disintegrated rock. The upper valve is almost always entire, and neither is 

 ever seen to be water-worn in the slightest degree. These considerations lead to the 

 inference that the bivalve in question may have existed in tho eocene period, con- 

 stituting another link in the important chain of connection between the secondary 



• Journiil cf the Atid^iny of NitunI Scienfw of Philadelphia, IMO. 



