﻿THE 



AMERICAN JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



Aet. XVIII. — A Post-Tertiary Elevation of the Sierra Nevada 

 shown by the River beds ; by Joseph LeConte. 



[Presented to the National Academy of Science April 24, 1886. Eead at 

 "Washington, May 3.] 



I have on several occasions alluded briefly to the evidences 

 of an elevatory movement in the Sierra at the end of the 

 Tertiary,* but I believe the subject is of sufficient importance 

 to deserve more special treatment. In the present paper I wish 

 not only to give the evidence more fully, but also and espe- 

 cially to correlate this movement with a contemporaneous move- 

 ment in other parts of the western half of the continent and 

 thus to show that it was very extensive. I wish to show that 

 tbe upward movement which seems to have affected all high 

 latitude regions at that time, but which was oscillatory and 

 therefore temporary on the eastern side of the continent and in 

 Europe, on the Pacific side ivas permanent, and has largely de- 

 termined the orographic structure of this side. 



* "Old river-beds of California," this Journ., vol. xix, p. 187, 1884. Science, 

 vol. iv, p. 64, 1884. Compend. of Geology, p. 374. Bichthofen in his "Natural 

 System of the Volcanic Eocks," p. 86, speaks of an elevation of the Sierra con- 

 temporaneous with the lava flood. In fact, according to him the Sierra region 

 was at that time changed from a gently hilly country to a great mountain range. 

 But his reason for so thinking is the supposed existence of the so-called Blue 

 gravel channel running parallel to the range. This channel is now believed to 

 exist only in the fervid imagination of old miners. 



Am. Jour. Sci.-— Thibd Series, Vol. XXXII, No. 1 89.— September, 1886. 

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