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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 800 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[1] 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:[2] "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 rejuvenescence of the vital enery of the rivers; the consequent downcutting of these to form the present deep cañons and the resulting wild, almost savage, scenery of these mountains."

The observations of Mr. W. Lindgren[3] 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 considerably 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

  1. ↑ Science, Vol. 1, March 23, 1883, pp. 194-195.
  2. ↑ Bull. Geol. Soc. of Am., Vol. 2, pp. 327, 328.
  3. ↑ Bulletin of the Geological Society of America, Vol. 4, p. 298.
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