10 GEOLOGY OF OHIO. 
shallowing and locally complete withdrawal of the Silurian Sea. Such 
material as composes the Oriskany might possibly be spread some dis- 
tance from the shore over the bed of that sea in its retreat, but the very 
decided contrast which the Oriskany presents, both in lithological char- 
acter and in fossils, to the underlying Helderberg limestones, indicates that 
it marks the dawning of a new era rather than the close of an old one, 
and that it was the first product of an incoming sea—the Devonian— 
rather than the last of the retreating Silurian. 
The Cauda Galli and Schoharie grits are universally regarded as Des 
vonian, since they contain many of the fossils of the Corniferous lime- 
stone; they are, in part, the shore equivalents of the open sea Corniferous. 
In the judgment of the writer, the Oriskany is the product of the earlier 
and wider spread of conditions similar to those in which the Cauda Galli 
and Schoharie beds accumulated; and that it is the true base of the 
Devonian system, corresponding in character and relative position to 
the Medina and Potsdam sandstones below. 
THE CORNIFEROUS LIMESTONE. 
This has proved to be one of the most interesting of all the rocks of 
Ohio, since it is a vast store-house of fossils, and these—especially the 
fishes and land-plants—hold a prominent place among the objects de- 
scribed in our volumes on paleontology. The Corniferous corresponds in 
general character with the Niagara and Cincinnati limestones below ; 
that is, it is the organic sediment formed from the débris of animal life 
which thronged the sea in the age of its deposition, and which slowly 
accumulated, by the processes of growth and decay, over all the area where 
deep and clear water prevailed in the submergence that occurred in this 
age. 
Many new species of fossils have been found in the Corniferous lime- 
stone sinee it was described in our first volume, but no facts have been 
observed which require any important modification of the view presented 
in that volume in regard to its distribution, history, and the life of the 
period in which it was deposited. Some interesting additions have been 
made by Professor Nelson to the collection of land-plants found in the 
Corniferous limestone at Delaware and Sandusky, and which we have 
conjectured once formed part of a luxuriant vegetation that covered the 
Cincinnati island in the Devonian Age, the first land flora of which we 
have any traces in the United States. These will be described more 
fully in our third volume of Paleontology. 
It will be remembered that the Corniferous limestone in Ohio consists 
of two divisions: a whiter and more massive member below, which we 
