(jo The American Urologist. August, L903 
tinned existence of the denizens of the clear warm waters of 
the Corniferous and Corniferous-Hamilton seas, and so to han- 
dicap them in the struggle with a competing fauna, if ready to 
invade their area. 
Two causes so important and so far-reaching- as these hiust 
have at least powerfully aided in bringing about the change 
of fauna, at the close of the Hamilton period, which the theory 
of professor Williams is intended to explain, and possibly they 
were of themselves sufficient to accomplish it. The conditions 
of life — the environment — are more powerful in determining 
the fauna of a region than the mere possibility of communica- 
tion, and if the Eurasian Devonian fauna was already as near 
as Nevada and western Canada, it might simply, by the changed 
conditions of the water and the bottom in the Appalachian gulf, 
be enabled to successfully invade that territory and to displace 
to a considerable extent its original occupants. 
This physico-geographical contribution to the subject may 
serve as an additional means of explaining the substitution of 
the Upper Devonian fauna of Eurasia, in Appalachia, for that 
which was the direct descendant from the previous occupants 
of the same region. 
D. THE OHIO SHALE. 
All over the upper limits of the Corniferous-Hamilton in 
Ohio. and the true Hamilton in the east of Appalachia lies that 
great mass of soft material which has been known as the Ohio 
shale. Generally speaking, this stratum is the equivalent of the 
Genesee, Portage, Chemung and Catskill of the east. It con- 
sists, in Ohio, of three more or less distinguishable parts, the 
middle one of which is the most massive and thickens rapidly 
from its outcrop in central Ohio to the eastward. A few local 
and thin sandstones of the "blue-stone" type are intercalated in 
the shale, but taken as a whole in Ohio and the adjoining re- 
gion it is a soft mass, in which the auger descends at the rate 
of ioo to 150 feet daily. To the eastward the sand increases 
both as a diffused ingredient of the shale and as bedded rock 
and these included sheets of harder and porous strata are the 
oil and gas reser.voirs of Pennsylvania and are known as the 
oil-sands. Beyond this to the east the shaly element further 
diminishes and the strata gradually merge into the almost pure 
sandstones of the Chemung and Catskill of the region. 
