THE NATIONAL INSTITUTION. 
191 
Bivalves. Bivalves. 
Mytilus hamatus, Say. Solen ensis, Lam. 
Nucula limatula, Say. Venus mercenaria , Lam. 
Nucula acuta, Conrad, 
The entire thickness of the tertiary clays has not been determined, but it has 
been ascertained that they sink to a very considerable depth, enough to convey the 
idea of a vast period of time elapsing between their origin and final deposition. 
Deep harbors and bays seem to have been filled up by the very gradual accumula¬ 
tion of fine silt or mud; generations of shells were entombed in frequent succession, 
until the harbors, bays, or part of the ocean itself shrinking into shallow lagoons, 
no longer furnished the conditions necessary to their increase, and myriads of oys¬ 
ters took possession of their deserted beds. There is no pause, no interruption to 
this ceaseless mutability. Our harbors and our bays must, in the lapse of ages, be 
filled up by the unfailing influx of silt; our present beds of oysters be converted 
into dry banks of shells. New bays will succeed to those which we now behold ; and 
other lagoons will encroach upon the sea. Whoever attentively examines the lo¬ 
cality last described, on the Potomac river, will be forcibly reminded of the mutability 
of the present features of our earth; he can read distinctly the history of the 
past, and anticipate, in a measure, the annals of futurity, the new order of things, 
the relative condition of sea and land yet to be, long after he has passed away, and 
his name, his influence, his labors having left no more trace of his existence than 
the “baseless fabric of a vision.” 
In Silliman’s Journal of Science and Arts, I have noticed a spot on the Neuse 
river, in North-Carolina, of more than ordinary interest, in consequence of the quan¬ 
tity of bones of land animals which are mingled with the upper tertiary shells. 
This place is about fifteen miles below Newbern, on the left bank of the river, and 
the two formations of medial and upper tertiary are in juxtaposition. The former, 
when I visited the spot, was concealed from observation, the excavations having 
been filled up, and the beds being nine feet beneath the level of the Neuse. Mr. 
Benners, who owned the land, informed me that all the bones were above this for¬ 
mation, mixed with the upper tertiary shells. These remains are nearly all water 
worn, black and silicified, and have evidently been transported from a distance, pro¬ 
bably carried by ice down the ancient Neuse, and dropped among the shells of the 
upper tertiary period. The bank of the river is here not in any part more than 
twenty feet high. The surface of the fossilliferous portion is very irregular, rising 
in a few places to the height of ten feet above the river. Its visible part consists 
of a mixture of sand and clay, in which are imbedded immense numbers of Mactra 
lateralis , and abundance of Solen ensis, towards the top of the stratum. The shells 
with two exceptions, are such as now exist on the southern coast of the Atlantic, 
and in the Gulf of Mexico, and the evidence of a climate very similar to that of 
the locality last described on the Potomac, is perfectly satisfactory. The Gnatho- 
don occurs here, and the whole group is very well represented in the Gulf of Mexico 
at the present day. 
List of Fossil Shells at Bcnners's. 
Univalves. Univalves. 
Buccinum trivittatum , Say 0 Fulgur canaliculatus. 
