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University of California. 



[Vol. 3. 



it would have been entirely obliterated, and nothing left to 

 suggest even the fact of its former existence. That the process 

 has proceeded thus far for most of the Great Western Divide 

 there can be but little doubt. It appears to the writer that we 

 have an illustration of it in the portion of the divide shown in 

 Plate 45 b. Here the divide is broad and massive, but is traversed 

 by a series of shallow glacial troughs running transverse to its 

 trend and separated by acutely serrate, narrow ridges. The 

 shallowness of these troughs is relative only. They are in 

 reality as deep as the cirques of the region usually are, but their 

 great length and breadth give them a shallow aspect. It is very 

 probable here that the intersection of the opposing slopes of the 

 transverse troughs has obliterated a plateau similar in character 

 to that west of Mt. Vandever. 



HISTORICAL ARGUMENT AND RESUME. 



The granites of the region are intrusive in rocks which, as 

 the fossils collected by Becker indicate, are of Triassic age. 

 They may, therefore, with little hesitation be regarded as having 

 originated at the time of the intrusion of the granites of the more 

 northern portion of the range, and these are of post-Jurassic 

 age. The granite of the Sierra Nevada thus appears to be a 

 vast batholith coextensive with the range. Remnants of the 

 roof of this batholith are abundant in the northeim Sierra 

 Nevada, but occur only as mere fragments in the southern part 

 of the range. The Mineral King belt of sedimentaries is one of 

 these fragments. One of the most important facts which the 

 relation of these rocks to the granite reveals is that, whatever 

 may have been the basement upon which they were deposited, 

 there is now no trace of that basement remaining. It has either 

 been resorbed by the granite or has sunk into it. The Mineral 

 King belt, as a whole, is sunk at least a mile in the granite, with 

 approximately vertical, sometimes overhanging, contacts on 

 either side. 



The mountain range, established at the time of this granitic 

 invasion at the close of the Jurassic, has persisted as a barrier 

 between the marine basins on the west and the land area of the 

 present Great Basin ever since. By the close of the Tertiary it 



