46 THE JOURNAL OF GEOLOGY. 



maintained by Whitney and others that the principal upheaval of 

 the Coast Range occurred at the close of the Miocene. 



At the northern end of the valley the elevation of the base 

 level is 8oo feet. To the eastward it rises gradually to 1,300 and 

 1,700, and finally in the neighborhood of Round Mountain to 

 2,500 feet, showing elevation in the Lassen Peak and Sierra 

 Nevada region east of the Sacramento valley. 



Mr. G. K. Gilbert^ was the first to recognize the broad plateau 

 upon the western slope of the Sierra Nevada as a plain of erosion, 

 and discussed the matter in such a way as to show that the height 

 of the range has been considerably increased since the erosion 

 plain was formed. 



Professor LeConte advocated essentially the same view. He 

 says ■.'^ "The rivers, by long work, had finally reached their base 

 levels and rested. The scenery had assumed all the features of 

 an old topography with its gentle flowing curves. At the end of 

 the Tertiary came the great lava streams running down the river 

 channels and displacing the rivers ; the heaving up of the Sierra 

 crust block on its eastern side, forming the great fault-cliff there, 

 and transferring the crest to the extreme eastern margin ; the 

 great increase of the western slope and the consequent rejuve- 

 nescence of the vital energy of the rivers ; the consequent down- 

 cutting of these to form the present deep cafions and the result- 

 ing wild, almost savage, scenery of these mountains." 



The observations of Mr. W. Lingdrens in the region of the 

 Yuba and American rivers upon the western slope of the Sierra 

 Nevada, " appear to prove that the grades of the remaining 

 Neocene gravel channels are to a certain extent determined by 

 the directions in which they flowed, in such way as to strongly 

 suggest that the slope of the Sierra Nevada has been consider- 

 ably increased since the time when the Neocene ante-volcanic 

 rivers flowed over its surface. It finally appears probable, from a 

 study of the grade curves of the remaining channels, that the 



^Science, Vol. i, March 23, 1883, pp. 194-195. 



= Bull. Geol. Soc. of Am., Vol. 2, pp. 327, 328. 



3 Bulletin of the Geological Society of America, Vol. 4, p. 298. 



