THE CARBONIFEROUS SYSTEM. 
lies within 400 feet of the Conglomerate. Here, as at Bradford and 
Kinzua, it contains numerous fossils, mainly of Lamellibranchiates; but 
in the valley of Oil Creek also some brachiopods which are character- 
istic of the Waverly in Ohio. Though becoming, as a general rule, more 
argillaceous, this formation is quite persistent, and.makes up the great 
mass of the Waverly group as it appears within the limits of our State. 
Ath. The Umbral shales of central Pennsylvania rapidly diminish in 
coming west, and either blend with the underlying Vespertine or totally 
disappear before crossing the Ohio line. From the fact that these shales 
contain almost no fossils in Pennsylvania, it is difficult to separate them 
from the Vespertine group, when changed in color and assimilated in 
composition to that group, as they are in their westward extension. 
5th. The Carboniferous Conglomerate is more persistent in thickness 
and character than any of the formations that have been enumerated ; 
and although exhibiting considerable variations in thickness, it may be 
considered as forming a continuous sheet, stretching from central Penn- 
sylvania to central Ohio. 
The section afforded by the Waverly, or Lower Carboniferous, rocks in 
northern Ohio is as follows, beginning with the summit of the series: 
The Conglomerate. 
Ieee Cuyahorai Shaler. cic Mecses.. 150 to 250 feet thick ) 
PREUUIRCEEA GET IL aoe roeh dortoeca Come olcmececes 60 ‘ 
Bi pedrord Shalen a sl uue mn flee oe Waverly Group. 
Arana C@levelandiShaleviess k.scsscessesccess 21 to 60 fs 
Erie Shale. (Chemung.) 
1. The Cuyahoga Shale.—This stratum immediately underlies the 
Conglomerate, and forms the walls of the gorge of the Cuyahoga river 
from Cuyahoga Falls to the Peninsula, and the upper part of these walls 
from that point to the vicinity of Cleveland. It also forms the surface 
rock of a large part of Medina county, the southern part of Lorain and 
Cuyahoga, and all the region about Warren, in Trumbull county. In 
this section of the State the Cuyahoga shale has a thickness of from 
100 to 250 feet, attaining its maximum development in Medina, Lorain, 
and Ashland counties. 
The prevailing lithological character of the deposit is that of a gray,. 
argillaceous shale, with thin, interpolated bands of bluish, fine-grained 
sandstone. In some localities, as at the Big Falls of the Cuyahoga, these 
layers of sandstone are very much thickened, and form massive beds, 
which may be used for architectural purposes. 
In passing from the valley of the Cuyahoga west and south, the Cuya- 
hoga shale is found to undergo a change of color and texture, becoming 
gradually lighter, until it approaches in tint the prevailing type of the 
