40 THE JOURNAL OF GEOLOGY. 



upon the baselevel of the Klamath Mountains, while in the oppo- 

 site direction it appears to stretch up to the high plateau at the 

 northern end of the Sierra Nevada, and shows the features 

 already noted of tapering abruptly to the edge of the baselevel 

 plain. This formation might be considered a fringe to the base- 

 level, and evidently was deposited at least in part during the 

 baselevel period. 



The earlier auriferous gravels upon the slopes of the Sierra 

 Nevada are older than the volcanic flows of the same region. 

 They are regarded by Messrs. Turner and Lindgren and the 

 writer as of essentially the same age as the lone formation in 

 the Great valley of California. The auriferous gravels were 

 accumulated and deposited upon the flanks of the range, while 

 the finer material, sand and clay, were carried into the Sacra- 

 mento valley. 



AGE OF THE BASELEVEL OF EROSION. 



The age of the baselevel must be determined by reference 

 to the formation with which it is associated. It is evidently of 

 more recent origin than the Cretaceous, since it truncates the 

 upturned edges of the Shasta-Chico series, and these are the 

 voungest strata upon which it has yet been seen. It was already 

 developed at the time the earlier auriferous gravels were 

 deposited, for they lie in the broad shallow valleys which belong 

 to the baselevel plain. The erosion by which it was developed 

 therefore occupied a part or the whole of the time interval 

 between the upheaval of the land at the close of the Chico 

 epoch (Cretaceous) and the deposition of the auriferous 

 gravels. 



The age of the earlier auriferous gravels has not yet been 

 fully determined, although they have been the subject of much 

 investigation. That of the later gravels will not be considered 

 here. Professor J. D. Whitney, in his "Auriferous Gravels of 

 the Sierra Nevada of California," page 283, says: " It appears 

 probable, on stratigraphical grounds, that the detrital beds over- 

 l3ang the bed rock of the Sierra Nevada represent the whole 



