RIVER TERRACES AND GLACIAL SERIES 439 



a serpentine 4X4X5 feet. The remarkable feature of this ser- 

 pentine constituent is that serpentine does not occur in place 

 anywhere in the basin of the (?/(af Salmon River between this point 

 and its head. The evident source of these bowlders is a ser- 

 pentine area on the eastern side of the old Coffee Creek valley, 

 within several miles of its head. That portion of the old Coffee 

 Creek valley has been captured and is now drained by Salmon 

 River. A study of the gorge at the head of the old Salmon 

 River valley indicates that the beheading occurred late in the 

 glacial period, that is, was associated with one of the later 

 glacial stages as will appear later in this paper. Salmon River 

 now has access to the serpentine and is bringing a small per- 

 centage of serpentine pebbles and cobbles below the gorge, but 

 they are soon worn out so that at the distance of three miles 

 from the gorge they are extremely rare in the present river 

 deposit. One so rarely finds a specimen of them in the old chan- 

 nels up to this deposit under discussion, that they may be con- 

 sidered practically absent. Why are they so characteristically 

 abundant in this higher and older gravel? I have but one 

 plausible explanation of it. A glacier headed in the old Coffee 

 Creek valley, overrode the col at the head of this valley and 

 sent a shallow tongue far beyond any point reached by sub- 

 sequent glaciations — three miles farther down the valley than 

 the distinct glacial moraines to be described later, and to a 

 locality now but 3,700 feet above the sea. 



Whether this is a glacial or a river deposit, I am going to refer 

 its level to Channel A. I am going to show traces of the same 

 deposit for several miles up the valley at nearly a uniform level. 

 They seem to have been deposited on the valley floor where it 

 joined the steeper mountain slope. Therefore, I consider them 

 to represent the level of the valley floor of that time in much 

 the same way as do the old channel deposits. 



In this deposit along the Spooner ditch all the granite bowld- 

 ers are thoroughly rotted to the core. So they are in certain 

 portions of the lower channels. But here other rock species 

 which are not usually much decayed in the river channels, fall to 

 dust. Various porphyries, diorites, gabbros, and schists will not 



