410 J. E. MILLS — ROCKS OF THE SIERRA NEVADA OF CALIFORNIA. 



laps far southward by the southern end of the western, and is much the 

 Larger mountain mass of the two.* It culminates near its southerly end 

 in mount Whitney, at an elevation of between 14,000 and 15,000 feet f 

 above sea-level. Its crest falls northward and, as a continuous crest, 

 terminates on the southern side of the Middle fork of Feather river. This 

 division of the range continues, however, northwestward from that stream 

 in broken sections to the edge <A' the great lava field west of Big meadows. 

 Besides being separated by the depression of the Middle fork of Feather 

 river, it is farther divided crosswise by the canyon of the East branch of 

 the North fork and the canyon of the main North fork of the same river. 

 It is known next north of the Middle fork as drizzly ridge, then ;is 

 Hough mountain or mount Hough, and north < if the East branch of the 

 North fork as Green mountain. It loses its distinctness as a topographic 

 feature north of the East branch, and ends north of the main North fork 

 west of Big meadows, near Prattville, where the metamorphic rocks pass 

 under the Tertiary lavas. The ranges east of the main crest and of the 

 mountains just named are here considered as belonging to the Basin 

 ranges. 



The western division is highest near its northern end, and is most dis- 

 tinct topographically between the Middle and North forks of Feather 

 river.']: It rises there to 6,990 feet above sea-level at Spanish peak. It 

 falls rapidly southward and, as a topographical member of the present 

 range, disappears, merging into the western slope of the eastern division. 

 Geologically, it can be traced to American river, if not farther southward, 

 by the outcropping of granite and other older rocks of the series. Still 

 farther southward the main western division is replaced by two or more 

 minor uplifted masses on the western slope of the eastern division. 



The duality of the northern part of the range is a very important geo- 

 logical feature. Each of the two divisions has its own axes, or, more 

 accurately, its own areas of habitual greatest uplifting ; and before the 

 Mesozoic upheaval the two were separated, at least during the period of 

 subsidence that preceded the upheaval, by an arm of the sea. 



Approximate Coincidence of successive Axes of Uplift. — The present relief 

 of the range, or at least of the northern half of the range, is due princi- 



*Tliis duality was recognized and, in a general way. described by Amos Bowman in a paper on 

 the "Geology of the Sierra Nevada in its Relations t<> Vein Mining," published in the 7th Annual 

 Report on Mineral Resources west of the Rocky Mountains by the U. S. Commissioner of Mining 

 Statistics, 1875. 



f " Hence we conclude that it is highly improbable that mount Whitney should be less than 14,650 

 feet high." J. D. Whitney, in Auriferous Gravels of the Sierra Nevada, 1879, p. 28. 



J The western division of the range really lies along an extension southward of the axis of the 

 Cascade range, and in a strict geological sense belongs to that range rather than to the Sierra 

 proper; hut it is probably impracticable to change the nomenclature so far as to make it eon form 

 to geological requirements in this respect. 



