162 THE ICE AGE IN NORTH AMERICA. 



The most interesting collection of facts appears in the 

 vicinity of Warren at the junction of Conewango Creek and 

 the Allegheny River. With little doubt the preglacial drain- 

 age flowed from some distance south of Barnesville northward 

 through Clarendon and Warren into the Conewango and 

 thence on into the Lake Erie basin, and at a level considerably 

 lower than that of the present river. 



The rock trough of the Conewango is much wider than that 

 of the Allegheny for several miles up the stream, showing that 

 the preglacial drainage was through the Conewango. This 

 greater breadth continues down the Allegheny to Irvine, and 

 thence up the Brokenstraw to the glacial limit. Below Irvine 

 the trough of the Allegheny again becomes constricted through- 

 out almost its entire course. Usually its lower rocky trough 

 below this point is not more than three-fourths as wide as it 

 is above Irvine, and at one point near Parker its width is 

 less than half that in the upper part of the valley. 



But the broad preglacial trough of the Conewango ex- 

 tends across the Allegheny through Stoneham and Clarendon 

 to Barnesville. The gravel deposits here are of the most 

 interesting and significant character. East of Warren upon 

 a rock shelf 250 feet above the present stream there is an 

 extensive gravel deposit from twenty to fifty feet in thickness, 

 containing many Canadian pebbles, and continuous with 

 and forming a part of undisturbed gravel strata extending 

 down the side of the trough to the river level. It is note- 

 worthy also that the lower part of this deposit for a consider- 

 able depth is fine sand, and at the bottom blue clay, indicating 

 deposition in stil 1 water. Crossing the Allegheny to Stoneham 

 we find here also a gravel deposit overlying deposits of fine 

 sand and blue clay containing frequent logs of trees such as 

 now cover the hills, and extending to a depth of 160 feet 

 below the surface in the middle of the trough. South of this 

 is a cranberry swamp two or three miles in length extending 

 to Tiona, where we again meet a gravel deposit filling a 



