Tertiary Strata of the Atlantic Coast. 105 
latitude, the proportion of those inhabiting between the tropics, grad- 
ually increasing to the southward, until we arrive at the extremity 
of the Florida peninsula, which, swept by the Gulf stream, is sup- 
plied with most of the West Indian species. The fossils, if they had 
been exposed with this uniformity, might be expected to correspond 
in the recent species they embrace, with those of the opposite coast, 
as is partly the case in the newest tertiary strata ; the species also would 
gradually assume a different general character, embracing more trop- 
ical species as the formations stretched to the south. The zoologi- 
cal characters of even the newest tertiary beds, are at variance with 
the phenomena we might expect from a sudden and universal eleva- 
tion. Throughout the tract I have alluded to, a bed of the common 
oyster, (Ostrea Virginiana,) very frequently occurs, with a few 
other shells now common in our estuaries and lagoons, and embracing 
occasionally small fragments of extinct species. These last have 
evidently been washed out of the older strata beneath, and the con- 
clusion is obvious, that the first upheave of the older strata in the 
open sea, has not elevated them all above the surface, but by ex- 
posing shallower portions of the bed of the ocean, a chain of la- 
goons or bays, as they are improperly called, was formed, in which 
the oysters accumulated, as they do at present in similar situations. 
The beds of these lagoons, have there been exposed, and wherever 
they occur, they will be found to overlie the oceanic reliquie of the 
medial Pliocene, having clearly been a more recent deposit. The 
organic remains below these are imbedded first, in the ascending or- 
der, in a lead colored clay, the thickness of which is undetermined, 
and next in sand, never exceeding fifteen or twenty feet in thick- 
ness. This alternation of clay or shelly marl and sand enclosing 
similar species is analogous to cotemporaneous strata in England ; 
of the Apenines, and of Sicily. The clay or marl exhibits no trace 
of having been subjected to the action of violent currents, but the 
Superincumbent sands always exhibit, more or less, evidence of such 
disturbance. In the newer Pliocene, angular fragments and water 
worn specimens of shells are found, and on the James river, in Vir- 
ginia, the matrix of the medial Pliocene contains perfect and delicate 
fossils, but is itself, in many instances, little else than shells commi- 
nuted by attrition. I infer, therefore, that the upper strata have 
been deposited in much shallower water, and that the deep sea de- 
posit of clay has been upheaved prior to the deposition of the form- 
er. The only locality I am acquainted with, where the clay does 
Vou. XXVIII.—No. 1. 14 
