18 GEOLOGY OF OHIO. 
are much finer and more impervious than in Pennsylvania, and are with- 
out the layers of sandstone and conglomerate which, on Oil Creek, serve 
as reservoirs for the oil, and also that the rocks of Pennsylvania are more 
disturbed than those of Ohio. This latter statement is denied by Prof. 
Lesley in his note to the report of Mr. F. A. Randall, On the Geology of the 
Vicinity of Warren, where he says: ‘The district of greatest oil produc- 
tion of Pennsylvania is precisely the district where there has never been 
any disturbance whatever. * * * In fact, had not Western Pennsyl- 
vania been lifted from the ocean bed into the air at the end of the coal 
era in a steady and gentle manner, without disturbance, the oil production 
would never have been a historical event.” Such a statement, coming 
from such a source, is not a little surprising, for every geologist knows 
that the great disturbance which formed the folds of the Alleghany 
Mountains was felt throughout Western Pennsylvania, and we have con- 
clusively proved that its influence extended even into Ohio. The series 
of basins which the Coal Measures exhibit in and immediately east of 
the oil region, are indisputable records of just such disturbance of their 
original horizontality as are indicated in the remarks referred to. That 
these disturbances were slight compared with those that affected the cen- 
tral portion of the Allegheny belt is evident; that they were sufficient 
to fracture and loosen rigid sandstones will hardly be denied by any one 
who knows any thing of the structure of the country under consideration 
and the condition in which the “oil sands” that underlie it are found. 
The experience of all the well-borers has shown that these are cracked 
and fissured in every direction, and their capacity as reservoirs is thereby 
greatly increased. As they were once unbroken sheets of sand and gravel 
their present shattered condition must have resulted from mechanical 
violence. That no disturbance could occur in the oil region without 
breaking up the strata and permitting the oil to escape, is a gratuitous 
and groundless assumption, for it is well known that a disturbance which 
would fracture and open the rigid sandstones, might leave the plastic: 
clay shales still impervious. 
CARBONIFEROUS SYSTEM. 
THE ERIE SHALE. 
As stated in the description of this formation contained in our first 
volume—the name Erie shale was applied to the great mass of argilla- 
ceous shale which forms the shore of Lake Erie from the Pennsylvania 
line to Avon Point. This was shown by the investigations made in the 
first year of the existence of the Geological Survey to be the western ex- 
