i86 
K. F. Mather 
Across the valley northeast of Claylick, the steepening of the 
base of the southern slope of the hills is indicative of similar 
glacial stream action between the ice-front and the valley wall. 
The village of Hanover is in a valley which, at the maximum 
extension of the ice, must have been occupied by a glacial 
lake, as shown by the terraces found here at an elevation of 800 
feet. This lake was held up by the ice of two dependencies of the 
main sheet, one at either end of the valley. Its overflow and sub- 
sequent drainage conditions account for the channel at Py now 
occupied by the traction line and the old canal; this channel is 
similar in every way to the one at Af, already described, and must 
have had a similar history. 
j 4 n alternate hypothesis. It has been hypothecated that when 
the glacier advanced into the valley past Claylick the ice-front 
drainage would have had unusual erosive powers and might have 
channelled the divide area so rapidly that a lake condition did 
not exist long. It, however, is not conceivable that an ice-front 
stream would have been strong enough to cut a channel in the 
Black Hand formation a mile and a half long across a ninety 
foot divide without necessitating the ponding of th^. stream be- 
tween the ice-front and the crest of the divide. The large amount 
of cutting necessary in the development of this channel, therefore, 
precludes the possibility of its having been made during the ad- 
vance of the ice into the valley. 
The cause of the capture and reversal. The capture of the west- 
flowing drainage by the east-flowing Licking immediately pre- 
ceding the glaciation of this region — perhaps in the earliest stages 
of the Pleistocene period — is not discordant with our knowledge 
of conditions at that time. The close of the Pliocene is looked 
upon as a time of crustal movement, a critical period in the history 
of North America, Streams were turned from their courses in 
some places and nearly everywhere started on careers of increased 
activity.^® A slight differential tilting would have caused the Mus- 
kingum and its tributaries to increase their valley cutting, and the 
reversal of drainage would have followed as the result of stream 
adjustment. The gorge of the Narrows is located at one side of 
a broad open valley having a lateral extension to the north of the 
crest of the gorge walls; this mature valley, at this point, was cut 
Chamberlin and Salisbury: Geology^ vol. iii, p. 316, 1906. 
