280 On the Tertiary Strata of the Atlantic Coast. 
Arr. XVI.— Observations on the Tertiary Strata of the Atlantic 
Coast; by 'T. A. Conran. 
Tue new Pliocene formation, or that deposit which is characteriz- 
ed by recent species of shells, in many places contains nothing more 
than beds of the common oyster shell, resting immediately on the 
older Pliocene marls. It seems certain therefore that the convulsion 
which upheaved the latter had been insufficient to raise them to the 
level of the ocean; but if sand bars existed then, as was doubtless 
the case, the ancient margin of the sea would, by the protrusion of 
these bars above water, be converted into a chain of lagoons, such 
as line the coast at the present day. Here then, the oysters of the 
newer Pliocene or last tertiary era, would find suitable conditions to 
multiply, until they were in their turn upraised above the level of the 
sea. If we are inclined to adopt this theory, we should carefully 
examine whether any fragments of marine shells can be detected 
among the beds of Ostrea, to indicate that the sea beach of that era 
existed as a boundary of the supposed lagoons; for in many places 
the level of the beach would doubtless have been such as to permit 
it to be entirely submerged by the waves of a tempestuous sea. | 
find ample proof of this in the deposits at Easton in Maryland, where 
among the oyster shells which are entire, fragments of Pecten madi- 
sontous an extinct species, are abundant. ‘This is an interesting ex- 
ample, for the upper bed of the strata beneath is composed almost 
entirely of the Pecten Madisonius. 'This bed therefore. in the new- 
er Pliocene era was the only one which could be disturbed by the 
surf, and the shells first broken on the sands of the beach were af- 
terwards swept into the lagoon and deposited on the bottom. To ex- 
plain the phenomena which would be observed after a slight elevation 
of our coast at the present day, the following diagram is annexed. 
Bar Sea Beach Lagoon 
! 
Sa 
