INTERGLACIAL GORGES- 69 



A steep slope in the place of a vertical cliff is the rule. This south- 

 western wall also disappears under drift just below the reservoir. 



The large amphitheater (just outside the limits of Fig. 2) in 

 which the reservoir lies represents the old gorge again occupied by 

 the stream and locally widened to an unusual extent. Here the 

 gorge walls on the south are steep, but not vertical. On the north- 

 east side the wall appears in several places where small side streams 

 have cut through the overlying drift. It is generally a perpendicu- 

 lar cliff. 



The bottom of the old 600-foot gorge, as exposed in a number 

 of places, rises upstream at a rate slightly less than that of the pres- 

 ent stream. As a result, the bottom, which appears some 6 feet 

 above the stream at the pumping plant, reaches stream level at the 

 reservoir and lies below it farther up. Partly for this reason the 

 old gorge, in the upper part, becomes more and more indistinct. 

 Its general width, taking the mile of its course just described, is 

 from 500 to 700 feet at the bottom and perhaps 100 feet more than 

 this at the top, for the walls are not everywhere perpendicular. Its 

 relation to the broader glacial trough of Six Mile Creek valley is 

 well shown in the accompanying cross-section (Fig. 3), drawn to a 

 vertical and horizontal scale of 2,000 feet to the inch. The proJSle 

 makes evident the broad, U-shaped valley with the sharply cut 

 gorge in its bottom. This gorge was probably nearly filled by 

 drift during the various glacial epochs since its formation. In two 

 cases — -at the reservoir and south of Green Tree Falls — -it is still 

 drift-filled to the top; elsewhere the stream has cleared out a good 

 share of the drift. 



In two places on the gorge walls glacial striae have been found; 

 one has already been mentioned, the other is at the eastern edge 

 of the pond, just above the pumping plant. The striations show 

 clearly that the gorge has been covered by ice since its formation, 

 but it seems equally clear from the sharpness of the old gorge walls 

 in most places that the action of this ice was weak and did not 

 materially modify the form of the gorge except at the lower end 

 and where the exposure was particularly favorable. It would seem, 

 therefore, that the gorge must have been cut subsequent to the 

 formation of the broad U -trough of Six Mile Creek valley, in the 

 bottom of which the gorge Hes. Otherwise it probably would have 



