68 



JOHN LYON RICH AND EDWIN A. FILMER 



at the level of the previously described rock bench across the stream 

 just below. The rock bench and the rock island together are inter- 

 preted as the bottom of the oldest, or 600-foot, gorge. Proceeding 

 upstream about one-quarter mile one comes to a portion of the 

 valley where relations are very clearly shown (see map). Both 

 walls of the old gorge are revealed and the bottom is seen along the 

 southwestern edge and in two places near the middle of the gorge. 

 Proceeding still farther upstream along the northeast bank, one 



may follow a small stream 

 which enters the amphi- 

 theater from the east. 

 For a few hundred feet the 

 course is along a narrow 

 valley excavated in drift. 

 Then, suddenly, one comes 

 upon a nearly perpendic- 

 ular rock wall which the 

 stream has encountered in 

 its downcutting and over 

 which it falls in a cascade. 

 The rock wall is straight 

 and disappears at both 

 ends under drift. Follow- 

 ing southeastward along 

 the projected line of this 

 rock wall, one crosses a 

 hill of drift and soon comes 

 down to the continuation 

 of the wall on the other 

 side {B, Fig. 2). Here it is fully exposed, perpendicular, and about 

 60 feet in height. At the northern end of the exposure the gorge 

 wall is glaciated. The perpendicular cliff is smoothed and striated 

 in true glacial fashion (Fig. 5) . From here the gorge wall may be 

 traced almost continuously upstream to the postglacial gorge just 

 below the reservoir, where, after being crossed by the main stream, 

 it disappears under drift (near W). 



The southwestern wall may be traced with practical continuity 

 all the way. It is, in general, less steep than the northeastern wall. 



Fig. 5. — The glaciated rock wall of the 

 600-foot gorge disappearing under drift. From 

 a photograph. 



