HIGH GRADES OF OLD CHANNELS GENERALLY. 295 



or cross-belts of hard massive rocks. Such an influence no doubt exists, 

 but it is certainly not very marked in the modern rivers. In the lower 

 Sierra, in which the direction of the rivers for shorter distances only are 

 parallel to the range, it cannot be stated to occur to any considerable ex- 

 tent; the principal forks have a fall of from 30 to 40 feet to the mile in 

 whatever direction they run. In the upper Sierra the Rubicon river 

 runs for fifteen miles near and parallel to the crest line, but the grade 

 averages very high — about 150 feet to the mile. 



The grades of the intervolcanic channels must be left out of consid- 

 eration in endeavoring to ascertain whether the height of the range has 

 been increased since Neocene times, for it has been shown that their 

 erosive activity was similar to that of the present rivers, and that the 

 changes from the conditions of the earlier Neocene to those of today 

 took place or began to take place before the intervolcanic channel system 

 was established. Referring to Mr Browne's diagram of the grades of the 

 volcanic channels, it may be noticed that they in general show a strong 

 grade in whatever direction thev flowed. 



Perhaps the first fact that attracts the attention when the grade sheet 

 is studied is the remarkably steep grades prevalent. Down near the 

 great valley, as well as high up in the mountains, grades of from 60 to 

 100 feet and above are noticed; these are certainly not the grades which 

 would be expected in rivers depositing gravel in a country which, as 

 shown by the topography, had been subjected to a long-continued 

 erosion. 



A further study will, however, show that while all of the transverse 

 principal channels have a strong grade, most of the principal forks flow- 

 ing in a direction about parallel to the trend of the range have a com- 

 paratively slight grade. The most striking instance of this is furnished 

 by the Neocene South Yuba from Badger hill to You Bet. The sudden 

 increase in grade from Waloupa to Dutch Flat (Thompson hill), where 

 the river suddenly turns from a longitudinal to a transverse direction, 

 illustrates this relation of grade and direction in an especially suggestive 

 manner. A similar contrast is noticed at the junction of the North 

 Bloomfield with the Grizzly Hill channel, and the course of the South 

 fork of the American from Pilot hill to Diamond springs shows a strong 

 tendency in the same direction. The grade of the longitudinal Forest 

 City tributary is considerably less than that of the main river into which 

 it empties, and the uppermost course of the Neocene Middle Yuba from 

 Milton to Meadow lake in a longitudinal course slows a much lower 

 grade than would be expected. 



This generalization does not apply to all of the principal forks, bow- 

 ever, for the grade of the important tributary extending from Damascus 



