on the Geology of Fast Florida. A7 
to small fragments, when the shells fall out entire, and some 3 
them can readily be seen without a glass. 
The variations in the groups of shells may be in part owing 
to some difference in geological age, as the Hocene has unques- 
tionably newer and older members, as well as the Pliocene or 
other formations. But depositions in different depths of water 
and on different kinds of bottom have also caused local variations 
in the fossil contents of Eocene rocks. Much light could be 
thrown upon this subject by a careful investigation’ of recent 
species inhabiting different depths of water along the coast. The 
Miocene, however, could be still better illustrated by this means, 
because the deep-water species are precisely those which most 
abound in the Miocene and are most rarely seen upon the beaches. 
Thus while sailing in the Gulf of Mexico, I watched with inter- 
est such specimens from the bottom as the lead brought up, and by 
this means I obtained a new Corbula, a specimen of Dentalium 
coarctatum, which I believe to be the first living one found this 
side of the Atlantic, although it is a common shell in the Virginia 
Miocene. I obtained also Cytherea elevata and Nucula acuta, 
which are likewise common in Miocene deposits. All these are 
deep-water species, living at the depth of eighteen or twenty 
fathoms, which I never found: recent on the beach, and therefore 
they may fairly be cited as evidence of the fact that such Mio- 
cene localities as contain abundance of them, originated in water 
of similar depth. Other localities of Miocene contain quite differ- 
ent species, and beds of shoal-water origin can often be clearly 
made out. With regard to the Kocene, no doubt can be enter- 
tained that similar causes have produced similar effects. I hope 
to make out a line of demarcation between the older and newer 
Strata of the Eocene period that may be convenient in the study 
of this formation. Thus I propose the Numinulite’ limestone of 
St. Stephens and Clark county, Alabama, and 
at Claiborne, as Lower Eocene} inasmuch as they hold a few spe- 
cies intimately related to, if not identical with, cretaceous forms, 
and so far as we know, all the species are extinct. The extent 
of Savannah river in Georgia, between Savannah and Shell bluff, 
Contains two recent shells, Lithodomus dactylus and 'Trochus 
agglutinans, and is evidently a later deposition than the former 
rocks. I propose to term this, Upper Eocene, and very probably 
Prevalent limestone of Florida will be included in this division. 
