The Abandoned Shorelines of the Oberlin Quadrangle, Ohio\YJ 



sandstone, which it crosses at Elyria, forms a local base-level for 

 the river south of this place. 



In the last six and one-half miles of its valley, the fall of the 

 river is about seven feet, approximately a foot per mile. North of 

 the Warren shoreline, it discontinued down-cutting long ago; its 

 further work, in reference to the present base-level, will be entirely 

 lateral plantation, the process which has already widened the val- 

 ley in some places nearly a half mile. When the Lake Erie level 

 was inaugurated, this portion of Black river had a descent of 95 

 feet. 



in the interval of approximately five miles between the War- 

 ren and Whittlesey shorelines the initial slope was about 60 feet; 

 the fall of the stream is now about 70 feet; the gain in gradient is 

 a response to the Erie base-level. Much more erosion has been ac- 

 complished than would appear to be the case from these figures, as 

 part of the 80 feet of channel-cutting involves the resistant Berea 

 sandstone. The width of the main valley, its numerous tributaries, 

 and their maturing cross-section, show that the Whittlesey part is 

 much older than the Warren part of the river. 



In the Maumee section we would expect even greater evidence 

 of age. But here the time factor is offset by the hard rock the river 

 has had to work on; its valley is shallow, and there are few tribu- 

 taries. South of this highest shoreline, the surface is more creased 

 by stream courses with somewhat wide valleys. 



