20G W. LINDGREN — TWO NEOCENE RIVERS OF CALIFORNIA. 



to Michigan Bluffs is as heavy as that of the main river running in a 



nearly cast-west direction; nor does it apply to the lesser tributaries. 

 The one emptying into the upper North fork of the American river near 

 Russian ravine has a very heavy grade, although running nearly parallel 

 to the range. The same is true of the fragment of channel exposed south 

 of Cisco. The ( lanada Hill-Sterrett channel offers an interesting instance 

 of a steep Neocene gulch or creek running for some distance in a north- 

 easterly direction. 



Another fact deserves notice. The North Bloom field*channel up to 

 Moores Flat and the Dutch Flat-Lowell hill channel, in a corresponding 

 position further south, show extremely heavy grades which scarcely can 

 he sufficiently accounted for by harder rock-masses encountered. The 

 North Bloomfield channel cuts with a heavy grade through the same 

 siliceous slates over which the Blue Tent channel flows with a very slight 

 grade. A mass of hard rock is met with at Dutch Flat, hut between 

 Dutch Flat and Lowell hill the slates are not particularly resistant. 



Taking in consideration the fact that there is no essential difference in 

 the character of deposits between the longitudinal and transverse rivers, 

 the relation of grade and direction explained above is a strong argument 

 in favor of a considerable increase in the slope of the Sierra since the 

 time the ante-volcanic Neocene rivers flowed over its surface. 



This uplift was probably gradual and extended over a long period, 

 beginning at or shortly after the initiation of volcanic activity. The 

 evidence from the region of the first summit in the territory here described 

 appears to show that this disturbance ended about the time of the last 

 great lava flows, and that while subsequent elevation might have taken 

 place it has been of slight importance. It is necessary to add, however, 

 that the region of the second summit has not yet been sufficiently exam- 

 ined to warrant the extension of the last statement to the whole range in 

 this latitude. 



If this increase in slope be attributed to a simple tilting of a rigid 

 block, such as advocated by Professor Le Conte, if I understand him 

 correctly, a reduction of the channels to fairly uniform grades is impos- 

 sible; for if the range be supposed to be tilted downward so that the 

 transverse channels with slighter grades become nearly level, many of 

 tic other transverse channels in which gravels have accumulated will 

 still have a grade of 80 feet or more to the mile. The maximum amount 

 of tilting to the mile cannot in this case have been more than the mini- 

 mum grade of the transverse rivers, or from 60 to 7<> feet to the mile. 

 This would give a maximum increase of elevation of between ."..('.mi and 

 4,200 feet. 



If, on the other hand, the increase in slope has been effected by means 



