THE NATIONAL INSTITUTION. 
175 
distributed; Other fossils are very rare. I found a specimen of Plagiostoma du- 
mosum (Morton) attached to an oyster-shell, which appears to be the only evidence 
of the existence of that extinct genus in a tertiary deposit. Overlying this stratum 
is abundance of the same Ostrece, in about three feet thickness of sand, cemented 
by carbonate of lime. Large specimens generally have a water-worn appearance, 
and occur mostly in single valves; but I found a few whole, unworn, very perfect 
shells. The young, which are vastly abundant, are also free from any marks of 
attrition, but are almost universally with disunited valves. 
3. The next in order is a stratum of incoherent sand, of a ferruginous color, con¬ 
sisting of angular grains of quartz, and crowded with shells, in a fine state of pre¬ 
servation, which, though friable, may nearly all be obtained entire, by taking time 
and great care in collecting them. Here are about seventy genera, and rather more 
than two hundred species of organic remains. Those bivalves which have a strong 
ligament, as the Lucina and larger Crassatellce , generally have the valves in appo¬ 
sition and the cartilage still remaining. The Cytherea cequorea , which resembles 
C. suberycinoides, (Deshayes,) the most abundant fossil at Claiborne, very seldom 
has the valves in connection; but if there has been any disturbance, at the time of 
deposition, it has been insufficient to injure the most delicate angles and striae of the 
shells. Occasionally, specimens are found which still retain their colored markings. 
The surface of this stratum, where a portion of the sand has been washed away by 
rain, presents the aspect of a solid bed of shells. Near the base of it, whatever 
point was examined, a vein of soft lignite was present, and, what is remarkable, 
certain fine large univalves appeared almost confined to this lignite, as if it had 
been formed from vegetable substance, in the eocene ocean, to which these uni¬ 
valves were partial. Beneath this line, the sand is somewhat coherent, and many 
species of shells are more rare, whilst others are more abundant than above it.* 
4. This stratum consists of argillaceous limestone, more or less friable, and about 
forty-five feet in thickness. It contains a few obscure casts of shells, referable to 
species imbedded in the sand beneath. Scutella Lyelli is the fossil of most fre¬ 
quent occurrence, but is also in great abundance in the sand, whenever that is suf¬ 
ficiently coherent to preserve its form. This rock somewhat resembles the newest 
member of the cretaceous group, which I found six miles west of the village of 
Claiborne; but a very dissimilar group of fossils shows the difference in age at a 
glance; and at St. Stephens, on the Tombeckbee river, the latter passes under the 
lower tertiary beds, as seen in the precipitous cliff. 
At the base of the Claiborne section, we observe such a group of shells as lived 
only in the open sea. Estuary shells are more rare among them than is usual in 
marine deposits ; for currents setting into the ocean generally carry with them the 
dead shells of estuaries, which may be frequently observed cast up on the beaches 
of the present seas. The eocene deposit of the Paris basin contains, it is well 
known, one hundred and thirty-seven species of the genus Cerithium, which clearly 
indicate the ancient occurrence of an estuary or arm of the sea. Now, in the con- 
• In the sand I found the following fossils of the Paris basin : Solarium patulum , (Lam.,) S. canali- 
eulatum , (Lam.,) Bonellia terebellata, Sigaretus canaliculatus , (Sow.,) Calyptrcea trochiformit. (Lam.,) 
Pyrula tricarinata , (Lam.,) Avicula trigona , (Lam.,) Cytherea erycinoides , (Lam.,) Corbis lamelloict , 
Cardita planicosta, Fistulana elongata } Pectunculus pulvinatus . 
