RIVER TERRACES AND GLACIAL SERIES 447 



cier built its moraines directly across the old channel, compelling 

 the river to adopt a more northerly course and erode a new canyon. 

 The overwash gravel and bowlders from the glacier were dis- 

 tributed down Channel C to a point below Cooper's mine. Before 

 this was completed a cloud-burst in the basin of Crosby Creek, 

 formed the torrent fan which is so certainly traceable down the 

 main valley nearly to Summerville. The building of local debris 

 fans over Channel C was an especially characteristic feature 

 everywhere and we are now able to connect it with the glacial 

 stage represented by the maximum extension of the Brown's 

 Gulch glacier. I accept this as evidence of an abnormally moist 

 climate and heavy precipitation in the territory outside of that 

 involved by glaciation. 



We will now transfer our attention to the vicinity of the upper 

 falls of the Salmon River, in the gorge which marks the original 

 head of the old Salmon valley. Above the gorge, the fiat floor 

 of hornblende schist extends out into the broad valley lOO yards 

 as exposed by the river. Since the last or Wisconsin glaciation, 

 the river has carved in this rock platform a canyon 30 to 50 feet 

 deep, and 30 to 50 feet wide at the bottom, with steep, in places, 

 precipitous slopes Through the upward rise of this rock platform 

 and the high grade of the stream, the canyon has become probably 

 75 feet deep at the upper end of the gorge. A sort of terrace is 

 traceable from the edge of the glaciated platform down through 

 the gorge, particularly on the south side. Next to the river there 

 is a precipitous rock slope capped by granite bowlders. Back of 

 this there is a comparatively gentle slope, encumbered by huge 

 granite bowlders. Above this there is a very steep, rugged slope, 

 apparently unglaciated. The summit of the ridge is rounded, 

 smoothed and covered with erratics. The Salmon River glacier 

 in the last stage clearly overrode this ridge, and seemingly 

 spanned across the gorge to the ridge on the north, whose summit 

 it rounded and covered with glacial debris. The slopes within 

 the gorge are apparently unglaciated (so far as the last stage is 

 concerned) as ragged rock surfaces abound. But the bottom of 

 the gorge at that time was a U-shaped valley descending as rapidly 

 as the present river ; certainly it was not such a narrow, rocky 



