THE CARBONIFEROUS SYSTEM. 87 



lies within 400 feet of the Conglomerate. Here, as at Bradford and 

 Kinzua, it contains numerous fossils, mainly of Lamellihranchiates ; 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. 



4th. 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. 



1. Cuyahoga Shale 150 to 250 feet thick 



2. Berea Grit 60 " 



3. Bedford Shale 75 



4. Cleveland Shale 21 to 60 



Erie Shale. (Chemung.) 



■ Waverly Group-. 



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 



