50 THE JOURNAL OF GEOLOGY. 



the same way the gold, being heavy, and associated with the 

 quartz originally, accumulated in the same channels, while the 

 fine light detritus was carried directly to the Sacramento valley. 



In his paper on the ancient river beds of the Forest Hill 

 divide,^ Mr. Ross E. Browne classifies the auriferous gravel chan- 

 nel systems into three periods. The first period was prior to the 

 first important flow of volcanic cement, the second was contem- 

 poraneous with the series of volcanic cement flows, and the third 

 following immediately after the last important flow of volcanic 

 cement extends to the present time. He has called attention to 

 the predominance of quartz gravel^ and sand in the ancient chan- 

 nels of the first period, and remarks that " quartz is the only impor- 

 tant material contained in the belts (of slates) which is hard and 

 permanent enough to resist the destructive action of the current." 

 This is especially true when the auriferous slates are disintegrated. 

 It is possible therefore that the predominance of quartz in the 

 earlier gravels may indicate an earlier period in which the slopes 

 had less declivity and disintegration exceeded transportation.^ 

 The fact that in the Light's canon region of Plumas county the 

 gravel is underlain by a sheet of residuary material which was 

 formed before the deposition of the gravel is evidence in the 

 same direction. Furthermore, the sand deposited with the gravel 

 is rough, angular and unassorted, such as is derived from residu- 

 ary material near at hand, and records a period of gentler decliv- 

 ity during the next earlier epoch. 



The old channels of auriferous gravel of the first period are 

 in a measure characterized by the large size of the deposits. Ross 

 E. Browne states :'* " In a general way it may be said that the 

 channels of the second period differ from those of the first as 



^ Tenth Annual Report, State Mineralogist of California, 1890, pp. 437-439- 



^ See also J. D. Whitney's Auriferous Gravels of the Sierra Nevada, page 323, who 

 says " that in some localities the gravel is almost entirely made up of quartz boulders 

 and pebbles." 



3 Mr. Bailer Willis some time ago, in his study of the Appalachian region, came 

 to a similar conclusion, yet unpublished, to account for the predominance of quartz 

 pebbles in the conglomerate at the base of the Coal Measures. 



* Tenth Annual Report State Mineralogist of California, pp. 439-441. 



