RIVER TERRACES AND GLACIAL SERIES 449 



nificant notch, too small for such a stream as Salmon River to 

 have flowed through it for a single week. When the glacier 

 front fell back a mile, it formed another moraine which dammed 

 the broad valley and turned the drainage of the upper valley 

 through the gorge into the old Salmon valley. Therefore, I 

 place the inception of cutting of the canyon in the gorge at a 

 time very little later than the maximum extension of the glaciers 

 of the Wisconsin stage and consider this canyon not more than 

 one-third as old as that eroded since the maximum extension 

 of the Brown's Gulch glacier. 



Following the bowlder slope on the south side of the gorge 

 down the valley, its edge gradually gets higher above the river. 

 The bowlder strip becomes pretty steep, then rather suddenly 

 changes to a flat terrace, 150 feet above the river, and whose 

 surface has granite erratics about as numerous as on the floors 

 of most glaciated valleys. This apparently represents the floor 

 of a glacier and we have passed beyond the bowlders which have 

 rolled down from the mountain. The steep slope facing the 

 river is due to stream erosion. Half way to the river is a rem- 

 nant of another flat terrace, also encumbered with bowlders. 



Very shortly the glacial terrace gives out and we come to a 

 slightly higher and steeper slope which has no granite bowlders 

 and seems to be composed superficially of local debris. This is 

 bounded on the river-ward side by a steep bluff 200 or more feet 

 high. On this slope occur granite bowlders. The phenomena 

 indicate a glacial deposit upon which has been built up an allu- 

 vial cone of local debris. The river flows in a rather broad 

 canyon trenched below this level. 



This slope has an angle of about 15°. Its width from the 

 upper to the lower edge is about 400 yards. Following it down 

 the valley we find built on it a bowldery terminal moraine of the 

 Cohnrad Gulch glacier, which came down from a cirque on the 

 northern face of Mt. Courtney. Between this moraine and the 

 river the long slope descends to within 100 feet of the stream, 

 acquires granite bowlders, then becomes undulating and very 

 bowldery, and forms a distinct moraine which appears on both 

 sides of the river and has been cut through by a gorge probably 



