36 The American Geologist. July 1903 - 
they next yielded, so far at least as we yet know, they returned 
no more. 
But the changes were far from complete. Not all the Corn- 
iferous fauna were killed by the changed environment. Some 
adapted themselves to it and lived. Nor did the whole immi- 
grant fauna die off when the water cleared. Some of its mem- 
bers proved capable of holding their own and the mingled spec- 
ies lived on together. 
The Hamilton fauna, at least the Marcellus division of it, 
must have been settled in New York and Pennsylvania long 
before it appeared in Ohio. Where it originated is a matter 
for separate inquiry. There is no room for doubt that the 
migration was in a westward direction. Consequently the 
stratum of shale in Ohio on the Scioto cannot correspond in age 
with the base of the Marcellus in New York, but it must be 
correlated with some higher horizon. As the Marcellus ranges 
in that region between fifty and three hundred feet in thickness 
considerable latitude can be allowed. The facts warrant the 
statement that Corniferous conditions prevailed in Ohio 
throughout the whole of the Hamilton period in New York, 
with a few temporary and local interruptions marked by the 
beds of shale above described. 
The Hamilton Sea. — The only representative of the typical 
Hamilton of the east is, as we have seen, the thin marly band of 
shale cropping out at Prout's Station, in Erie county, from 
which Dr. Newberry has reported the following fossils* : 
Spirifera mucronata, Cyrtina Hamiltonensis, Strophodonta 
dcmissa, Athyris spiriferoides, HeliophyUum halli, Phacops 
bufo, Ancyrocrinus (probably bulbosus). 
It is needless to discuss the evidence of so characteristic a 
list of fossils as the above, but they have, so far as I am aware, 
been met with nowhere else in the limits of the state. The thin 
band of shale in which they occur is due in many other places. 
in fact wherever the junction of the upper limestone with the 
overlying shale is visible. But its non-discovery by no means 
proves its absence. So thin and soft a stratum might easily 
be overlooked even in outcrop or might be entirely obscured or 
removed by weathering. And in the process of drilling by no 
chance could such a bed be distinguished in the wilderness of 
* Geology of Ohio, vol. ii, p. 190. 
