432 OSCAR H. HERS HEY 



a rock bench with a flattened or channeled, water-worn surface 

 (the channel level) overlaid by 5 to 20 feet of river gravel and 

 this by a variable thickness of sandy clay and angular local rock 

 debris, the surface of which constitutes the terrace level. There- 

 fore, the height which I may give for a channel level is always 

 less than that of the corresponding terrace level. Where mining 

 has been carried on extensively, it is often difficult to determine 

 the original surface level of the deposit, but where there has been 

 no mining, the terrace level is the conspicuous feature. The 

 channel is by far the most constant and safest guide to follow as 

 the terrace level is locally raised by torrent fans from neighbor- 

 ing gulches. 



The South Fork of Salmon River, in this region, has a nearly 

 straight course (minor deflections excepted) from east to west, 

 being controlled by the predominant joint system of the horn- 

 blende schist into which it has trenched a narrow valley, 3,500 

 feet in depth. It has migrated southward with the dip of the 

 joints. In consequence, the channel remnants occur predomi- 

 nantly on the north side of the river. On the south of the river, 

 back of the immediately overlooking peaks, there is a group of 

 higher peaks, including Mt. Thompson (altitude 9,345 feet) and 

 Mt. Courtney (altitude about 8,800 feet). Within the shadow 

 of these peaks, there are a number of cirques, each of which, in 

 the glacial period, was the gathering ground of an independent 

 glacier. 



CHANNEL REMNANTS FROM SUMMERVILLE TO BIG BEND BASIN; 



The channel which comes up through the gorge below 

 Summerville at a height of 30 to 50 feet, upon entering the 

 Summerville basin seems to separate into two strands, of which 

 the first becomes lower, relative to the river, partly because of 

 partial filling of the channel by tailings, and spreads out to a 

 bench, on the north side of the stream, several hundred feet wide 

 (Channel E). Back of it, and apparently 15 or 20 feet higher, 

 there is another broad shallow channel (Channel D). As we 

 travel up through the basin, we find this latter occurring at 30 to 

 40 feetabove the river, on both sides. The canyon in it is unusually 



