INTERGLACIAL GORGES 71 



gravel. This delta deposit is well shown in a cut on the east side 

 of the road, where it was used for gravel. It lies at the general level 

 of the lowest large deltas of Coy Glen and Butternut Creek. There 

 is some evidence, not yet fully worked out, which points to similar 

 deposits as the cause of the diversion of the stream into the two 

 other postglacial gorges farther upstream. 



The postglacial gorges are narrow, with walls for the most part 

 vertical rock cliffs. The lower and upper of these gorges still 

 possess waterfalls and cascades. In every case they are distinctly 

 smaller than even the second of the older gorges. 



INTERPRETATION 



The interpretation put upon the series of gorges in Six Mile 

 Creek is that they were formed by the stream during interglacial 

 intervals. The sequence of events is interpreted as follows : 



1. Preglacial time. — The stream probably flowed in a broad, 

 mature valley, tributary to the Cayuga Lake trough. The bottom 

 of this valley may have lain at the level of the pronounced rock 

 bench which is clearly marked along the south side of the valley 

 between the 800- and the 1,000-foot contours. This bench is well 

 shown on the topographic map, and is brought out clearly in the 

 accompanying profile (Fig. 3). 



2. First glacial epoch.—The Cayuga trough, extending parallel 

 with the direction of ice movement, was greatly deepened by ice 

 erosion while at the same time Six Mile Creek valley was deepened 

 considerably and given the flaring U-form typical of glacial erosion. 

 The deepening of the Cayuga trough exceeded that of the Six Mile 

 Creek trough, leaving the latter hanging. 



3. First interglacial interval. — During this interval Six Mile 

 Creek cut a gorge in the bottom of its hanging valley. That gorge 

 is the oldest, or 600-foot, gorge, described above. The interglacial 

 interval must have been long, for the gorge was cut to an even 

 gradient throughout the whole extent now visible and was also 

 widened very considerably. As we have pointed out before, the 

 gradient of the stream that developed during this interglacial inter- 

 val was flatter than that of the present stream. An attempt was 

 made, by taking several points as definitely located as possible 



