UPPER OHIO DRAINAGE SYSTEM. 97 



north it gradualh' thins away, and where it enters the count_y has not more than 

 half that thickness, while at Wampum, 4 miles above, it is still further reduced to 50 

 feet, and on going north along the Beaver a few miles from that point it disappears 

 entirely as a massive rock, being reduced to a few feet of flaggy sandstone and shale. 

 After thinning awa}'' almost entirely on the Big Beaver near Newport, it comes 

 in again to the north below Newcastle, and is seen at the falls of Big Run, where it 

 is 30 to 40 feet thick and quite massive. It also retains its massive character to the 

 northward, along the Neshannock. 



As to the route pursued by the old drainage Kne from the head of the 

 Beaver toward the Lake Ei'ie Basin, the available data appear to indicate 

 the one from Edenburg northward past Harbor Bridge to Sharon, Pa , and 

 thence westward past Yoiingstown to the Grand River Basin. But as an 

 alternative view it is suggested that there may have been more than one 

 channel across the resistant portions of the Carboniferous conglomerate, 

 between the head of the Beaver and Youngstown. While the main cur- 

 rent followed the route suggested from Edenburg to Youngstown, a sub- 

 ordinate one may have opened a narrower but more direct channel along 

 the Mahoning Valley. The united breadth of these channels is scarcely 

 equal to the average breadth of the Beaver Valley. The possibility of 

 double channels being maintained during the opening of a deep valley 

 finds such striking illustrations in the present Ohio Valley that this view at 

 least merits attention in the interpretation of the drainage peculiarities. 

 Tlae difficulties of interpretation are intensified by the presence of the 

 glacial deposits, whicli have greatly obscured the valley contours and 

 buried the gradation plains. 



Although the gradation plain passes below the level of present 

 drainage lines near the head of the Beaver, its altitude and slope may be 

 interpreted with a fair degree of certainty by means of borings. In the 

 abandoned valley between Edenburg and Harbor Bridge farm wells enter 

 rock at about 800 feet above tide, or a few feet lower than the gradation 

 plain in the north end of the Beaver Valley. In the abandoned valley 

 between Sharon and Youngstown a boring at Hubbard enters rock at a 

 level slightly below 800 feet. Wells in the Grand River Basin near 

 Mesopotamia, only a few miles north from the present divide between the 

 Mahoning and Grand rivers, reach the rock at about 650 feet above tide, 

 and this probably marks the level of the old gradation plain. From the 



