MARGINAL GLACIAL DRAINAGE FEATURES 535 



of such a channel begins high up on the hill, if after the channel had 

 been started the ice continued to advance, the channel would soon be 

 covered and another farther up the hill slope would be begun. Such 

 reasoning strongly supports the belief that this channel was formed 

 by waters associated with a retreating ice-sheet. It was not, however, 

 formed during the final retreat of the last ice, for within the gorge 

 itself are deposits of glacial drift which the stream is still engaged in 

 removing. It has nowhere as yet reached rock bottom. The presence 

 of the drift clearly proves that, after the gorge had been cut to a depth 

 greater than the present, it was subjected to glacial action. 



The cutting of the gorge has introduced a hanging condition in the 

 streams A, B, and C (Fig. 4). The stream C, which, as the map 

 shows, has only a small drainage area, enters Cayuta Gorge without 

 falls through a drift-filled rock gorge thirty or forty feet in width. The 

 stream bottom, at least in the low^er part of the gorge, is entirely on 

 drift. The presence of this drift-filled tributary gorge shows that, 

 since the glacial epoch during which Cayuta Gorge was formed, there 

 came an erosion interval long enough for a small stream to cut a good- 

 sized rock gorge. After this period of erosion came another epoch of 

 glaciation during which the gorges were filled with drift. Since glacial 

 times this stream, working over a very steep grade, has been unable 

 to remove the drift from the gorge which in the interglacial interval 

 it had cut in solid rock. This w^ould indicate that the ratio of inter- 

 glacial to postglacial time is roughly that of the time taken by a stream 

 to cut a gorge in rock to that taken by the same stream to cut a gorge 

 of about equal size in drift. 



Stream B shows an even more complex history. It enters Cayuta 

 Gorge at a rather steep grade through a gorge which is distinctly 

 interglacial in character. Its walls are veneered with drift and appear 

 much weathered. The stream, which flows in a series of cascades 

 over a rock bottom seems to have deepened its channel in the rock 

 by about six feet since glacial times. One-fifth of a mile above its 

 mouth the gorge widens out into a nearly circular amphitheater (Fig. 

 5) at which there is an abrupt change in direction and an absolute 

 change in the character of the gorge. For one -half mile or more 

 above the amphitheater the stream flows with an even grade through a 

 rock-walled, partly drift-filled gorge at least three times wider than 



