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 the 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 w'as led to the comparison, in the first place, 
by discovering the Cardita phinicosla, 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 visionary, but the palaeontologist must acknowledge as useful and true. 
At Upper Marlborough, Prince George’s county, Maryland, and at other locali¬ 
ties in Maryland and Virginia, green-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. 
suraes the character of burr stone, and the shells which abound in it are beautifully 
silicified. Near Piscatawav 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— Ostrea 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 be peculiar 
to it. Pariopaa elongata 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, are identical with species of the lower tertiary at 
Claiborne, Alabama. The most interesting shell is Gryphaea vomer, ( Ostrea 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 in 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 Gryphaea scattered in abundance over the surface of the disin¬ 
tegrating rock, in company with the 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 \ T alves 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 in¬ 
sulted from the fragility of the 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 the eocene period, con¬ 
stituting another link in the important chain of connection between the secondary 
* Journal of the Academy of Natural Sciences of Philadelphia, 1830. 
