418 Miscellanies. 
and some Flustre. It is only two feet in thickness. Above this rests 
the depository of the fossils described in such abundance in the pres- 
ent work. The bed is seventeen feet in thickness. It is composed 
of a loose, quartzy sand of a brownish color: the grains of which 
are small and angular, and so slightly coherent as to permit the extri- 
cation of the most delicate of its imbedded shells. The next stra- 
tum distinguished, is only about eighteen inches in thickness, consist- 
ng of a friable rock, easily separating into irregular pieces, and like the 
subjacent one, composed of quartzy sand ; but whose grains instead 
of being angular, are rounded, being held together through the inter- 
vention of carbonate of lime. It contains casts of several shells, 
among which were detected, Avicula, Venus, Crepidula and Tur- 
ritella, Above this, reposes a thin layer, two feet in thickness, com- 
posed of sand and shells slightly adhering by means of an argillo- 
ferruginous cement which imparts a reddish brown stain to the aggre- 
gate. The calcareous matter of the shells is so much decomposed 
as to render it almost impossible to remove them from the surround- 
ing matter. Avicula, Venericardia, Nucula, Venus, Teredo and 
a few others were noticed among its imbedded fossils, as was also, 
the Scutella crustuloides (Morton.) ‘This layer and the preceding 
are therefore with propriety believed to belong to the same epoch 
with the stratum so rich in fossils, upon which they rest. Superior to 
these comes on, at the depth of forty five feet, the formation, com- 
monly called in. Alabama, ‘the rotten limestone.” 
It is an indurated marl containing scattered masses of dark green 
sand, and contains Corbule, Nucule and some other bivalves which 
could be identified with fossils in the three lower beds. ‘“ A small and 
very thin Pecten with delicate ribs seemed the only shell which left 
its trace in a calcareous state. On each side of the fracture a silvery 
whiteness marks the deposit of this thin and fragile species. Su- 
perior to the present stratum, which may be considered as the cap of 
the Tertiary, is found the Diluvium of the country, forming a mantle 
about twenty feet in thickness, composed of sand and gravel mingled 
with clay. 
Mr. Lea, unhesitatingly refers the rich fossiliferous stratum and its 
superior members to the same period as the London Clay of Fngland 
and the Calcaire Grossier of Paris, remarking, that this deposit is 
composed of siliceous sand, while that of the London Clay is argil- 
laceous and the Calcaire Grossier is calcareous. It will therefore 
fall within the Eocene period of Mr. Lyell. 
