6o BULLETIN OF THE LABORATORIES 



to the east of this basin. The Scioto lobe found the Ohio 

 shales of the northern watershed a rock easy to erode and so 

 a great low place was ground out of the watershed between the 

 preglacial Muskingum and the main drainage axis to the north, 

 in the region of Marion county. This material was carried to 

 the south and filled up to its present level the great valley of the 

 preglacial Muskingum. Its southward movement was checked 

 by the high hills of the southern bank of this valley, only the 

 low outliers being covered with drift and buried out of sight. 

 To the west the ice extended somewhat over these hills and 

 crossed the present Ohio above Cincinnati causing the deflection 

 and the cutting of the new gorge below the city which was also 

 subsequently invaded. The Scioto lobe on its eastern margin 

 heaped up the drift on which the Licking reservoir is located 

 and thus again dammed the old Muskingum channel. Its last 

 lateral and eastern expression is found in the Hanover dam. 



While the ice stood at its maximum great rivers of glacial 

 waters were poured off of the ice sheet, which backed the 

 waters up in all the southern tributaries of the preglacial Mus- 

 kingum, and the great waters set to the west cutting down one 

 after another of the cols separating these southern basins, and the 

 positions of the lowest gaps were probably represented by 

 nearly the present position of the Ohio river. As these were 

 cut through and the Ohio developed in this region, the same 

 thing was happening in its upper basin. As the channel deep- 

 ened great rivers from the melting ice developed the channels of 

 the present Muskingum, Hocking, Scioto and the numerous 

 channels in the Miami region by reversed currents. After the 

 retreat of the ice these channels were cut of sufficient depth and 

 the dams at Hanover, the Licking Reservoir, Urbana and 

 St. Paris were of sufficient height so that there could be no re- 

 turn to the preglacial systems. The drift accumulations were 

 so great in the main axial valleys that with the probable as- 

 sistance of some differential movements the whole upper drain- 



