98 The American Geologist. 
August. 1908. 
divisions. There is no natural base in the field for Dr. New- 
berry's proposed separation at the top of his Huron shale. 
And. where the Berea grit is absent, it is not possible to find 
in this region any distinct physical difference between the top 
of the Corniferous limestone and the sandstones of the Coal 
Measures. 
Correlation of the Shales. — Time and space forbid even a 
review of the many historical discussions that have taken place 
regarding the equivalence of the Ohio shale above the Cornif- 
erous-Hamilton and below the Berea grit. It must suffice to 
maintain that, as a whole, it is the contemporary of the New 
York series from the base of the Genesee to the top of the 
Catskill. 
First among the problems connected with the great shale 
may come the changes manifested from its outcrop in Ohio to 
the eastward. To illustrate this topic, the accompanying ser- 
ies of sections has been drawn up from well-records along a 
somewhat irregular line traced upon the corresponding map, 
extending from Findlay, O., to Potter county, Penn. The dia- 
gram shows the elevation of the surface above sea-level, the 
thickness of the strata penetrated and the depth of the bottom 
of each hole, with the probable correlation of the different 
strata. 
In thus attempting the correlation of the great shale of 
Ohio with the better differentiated rocks of Pennsylvania and 
New York, very great minuteness cannot be expected', on ac- 
count of the change in their nature and the difficulty of inter- 
preting with accuracy the numerous well-records on which most 
of the sections are based; and, lastly, on account of the impos- 
sibility of securing even these sections along the same straight 
line. Great allowance must therefore be made in the examin- 
ation of the diagram, and close criticism will doubtless dis- 
cover many points on which not only judgment will differ, but 
where the data may seem inconsistent. 
The first section shown — that at Findlay — lies west of the outcrop 
of the Ohio shale and begins at the Lower Helderberg limestone, on 
which lies elsewhere the lowest of the Devonian strata. It is the rec- 
ord of the famous Karg well, one of the very largest gas gushers that 
has ever been drilled on the continent, having a capacity of twelve mil- 
lion cubic feet per day. The Trenton limestone was penetrated to the 
