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PROCEEDINGS OF 
ternporaneous deposit at Claiborne, a mere trace of this genus was all I could find 
during a protracted investigation of the fossils. If we suppose, then, the lowest 
bed at Claiborne to have been deposited in the ocean, we must infer this to have 
been elevated until it was cut oif by a beach, and thus converted into a lagoon, 
because the group of oceanic shells was suddenly interrupted, and the Ostreoe began 
to congregate upon them in the land-locked and calm water. These, in their turn, 
were as suddenly banished by the sinking of the coast, which converted their 
harbor into the open sea, and restored the oceanic shells to their original po¬ 
sition. 
Although I believe the rise of land to have been generally by insensible degrees, 
through the agency of the crystallizing force acting throughout primary or grani¬ 
tic rocks, yet for this sudden interruption of groups from an oceanic to an estuary 
character, some other explanation seems necessary. Two theories only present 
any claim to our attention : one is, that a sand bar might have been suddenly 
formed by a violent tempest, which permanently remained to protect the shells in 
the lagoon; and the other, and perhaps more probable solution, is, that during an 
earthquake the land may have been suddenly elevated. The sea was cut off from 
its original beach by a bar, previously under water at all tides, but now constituting 
an embankment, which the ocean might never again be destined to pass. Of this 
conversion of sea into land-locked water, we see proofs everywhere throughout the 
three tertiary divisions, but of the conversion of the latter into the former, or sink¬ 
ing of the land, 1 am acquainted only with the solitary but interesting example at 
Claiborne. I know not in what estimation others may hold this phenomenon as 
evidence of the sinking of the land, but to my mind it appears as conclusive as the 
perforations of litkodomi on the columns of the temple at Puzzuoli, so admirably 
illustrated by Lyell. 
Classification of Tertiary Formations —-It is doubtful, in the comparison of ter¬ 
tiary deposits, whether the relative amount of recent and extinct species may not 
be carried to an extreme injurious to science, especially before all the fossil as well 
as the recent forms shall be obtained. In the strata above the eocene, especially, 
is great care requisite in this mode of comparison, as the groups vary so continually 
in localities separated by an inconsiderable interval, that the fossils of the one shall 
be nearly or quite all of extinct species, and those of another shall embrace several 
existing forms. Nor can there be any doubt of the synchronous nature of these 
deposits, when we refer to the medial tertiary formation, because, taking a gene¬ 
ral view of the palaeontology of the region, it is found to characterize a single era 
in the clearest and most satisfactory manner. Even when we trace the deposits 
in their horizontal continuation throughout a long line of coast, like that of the 
Chesapeake bay, we begin at one extremity, with a certain class of shells, which 
gradually drop some and acquire other forms, as we proceed towards the opposite 
termination of the beds, where there will be found scarcely a species in common 
with those at the spot where we commenced observation. In my first explorations 
in Maryland, I was greatly surprised to find a group of shells on the Choptank river, 
near Easton, which scarcely held a fossil in common with the localities I had pre¬ 
viously studied on the western Peninsula, yet I could not doubt the contemporaneous 
origin of all these beds ; and I subsequently found nearly the same group on the shore 
