438 OSCAR H. HERS HEY 



into solid rock lOO feet deep as a minimum. Over the gravel 

 there was stratified local debris 30 to 40 feet thick. 



The slight variation in height above the river, of the differ- 

 ent remnants of a given channel is due to the facts that the 

 river always has had a variable grade because of harder and 

 softer rock belts and that the present higher grade and lower 

 grade sections do not quite correspond with those of the past. 

 As a matter of fact, the older channels were better graded than 

 is the present river bed. 



In ascending the river from Summerville, Channel C gradually 

 approaches the present river level and the new canyon, at first 

 thought, might appear to be smaller. In reality, I have found, 

 to my surprise, that the river everywhere has accomplished about 

 the same amount of cutting in rock of a given hardness. The 

 new canyon above Big Bend basin is largely excavated to one or 

 the other side of the old course and includes the removal of 

 considerable rock above the level of Channel C. 



Along the old Spooner ditch on the north side of the valley, 

 overlooking the old channel remnant just described, there is an 

 area of gravel about 1500 feet in length and lOO to 200 feet in 

 width. Its lower edge seems to be about 300 feet above the 

 river, and it ranges to at least lOO feet higher. Near the western 

 end it seems to rest on a bed-rock slope of 10° to 20°, much 

 less than the slope above or below. The ditch is cut into it for 

 several hundred yards to a depth of about 10 feet and splendidly 

 exposes its interior. It is a heterogeneous agglomeration of 

 bowlders and pebbles and subangular rock fragments embedded 

 in a grayish (partly brown stained) sandy clay. There is no 

 sorting of the material and not a trace of stratification. Its 

 general appearance is that of a glacial deposit, but it is so old 

 and rotten that if any striae existed they have been destroyed by 

 decay. 



The larger bowlders are chiefly of hornblende schist from 

 the subjacent terrane, Courtney granite from near the head of 

 the river and massive serpentine. The latter are plentiful enough 

 to be conspicuous. Bowlders 18 inches to 2 feet in diameter are 

 found without much difficulty. The largest bowlder observed is 



