BEAVER RIVER DRAINAGE SYSTEM. 149 



County to the head of Grand River Basin near Warren, Ohio, through 

 which it formerly e^Hidently discharged. It now makes an abrupt turn to 

 the southeast along- a small valley which apparently headed near the Ohio- 

 Pennsylvania line. Smaller tributaries illustrate still further the unnatural 

 courses of the present lines of discharge. 



In connection with this drainage system, it is necessary to consider 

 several distinct fluvial plains. The gradation plains and rock shelves which 

 slope toward Lake Erie from the mouth of the Beaver ai'e the earliest of 

 the series. The gravel filling which built up the lower part of the Beaver 

 and the Upper Ohio sufficiently high to give a discharge down the present 

 Ohio comes next in the series. A rock floor cut to a lower level than the beds 

 of the present streams apparently fonns the next well-defined fluvial plain. 

 A gravel filling which occurred during the Wisconsin stage of glaciation 

 evidently succeeded the deep excavation of the valleys, and comes later in 

 the series. This gravel filling is now in process of excavation by streams 

 whose beds form the last of the series of fluvial plains. Attention will 

 be here directed only to the main gradation plain, to the rock floor buried 

 beneath the present streams, and to the gradients of the stream beds 

 The gravel fillings are considered in connection with their respective drift 

 sheets. 



The gradation plain has been greatly disguised by a di-ift coating, 

 except in the lower course of the Beaver. It apparently descends north- 

 ward along the Beaver and the Shenango, as outlined on a preceding page, 

 about to Sharon, Pa., but it does not appear to continue its descent along 

 the Shenango north of that city. At Grreenville, 25 miles above Sharon, 

 a series of wells test the valley quite widely and strike a rock floor, appar- 

 ently^ the old gradation plain, at a level about 35 feet higher than the level 

 of the old plain at Sharon. This condition fits in naturally with the inter- 

 pretation that the old drainage passed westward from Sharon into the 

 Grand River Basin. At Youngstown, Ohio, which is on the line apparently 

 followed by the old stream, the gradation plain appears to be lower than 

 at Sharon, though the valley has not been explored sufficiently to make 

 certain the precise altitude of the gradation plain. At Niles, also on the 

 old line, the rock floor in one boring was found to be 66 feet lower than at 

 any ascertained borings in the vicinity of Youngstown. Borings in the 

 Grand River Basin near Southington, Mesopotamia, and Rome, Ohio, have 



