A(IK OK MOCNTAIN BUILDING. 9 



of tlie Junissic pei'iod took place tlie t'oldin*;-, Hexing- and t'nulting of tlie 

 beds wliicli oiitliued the structural features of nearly all the meridional 

 ranges between the abrupt walls of the Wasatch and those of the Sierra 

 Nevada. At Eureka no direct evidence is offered as to the time when this 

 moimtain building took place other than that the region was finally lifted 

 above the ocean after the deposition of the IJppei' Coal-measures. So far 

 as the mountains themselves are concerned, there is a total lack of evidence 

 that the l)locking out of the ridges did not begin at the close f)f the Paleozoic 

 period, but, on the other hand, all observations tend to show that whenever 

 and by whatever causes the other Great Basin ranges were uplifted, the 

 same orographic conditions which prevailed elsewhere held true for the 

 Eureka Mountains. In othei- words, the Eureka Mountains were a part of 

 a more extended geological province. 



According to the conclusions of Mr. Clarence King,' l)ased upon the 

 observations of tlie geologists of the Fortieth Parallel Exploration, the 

 mountains west of the Havallah Range and the meridian of 117" 30' belong 

 to a post-Jurassic upheaval, and to the west of this line there existed during 

 Paleozoic time an elevated continental area which furnished the material 

 accumulated in an ocean basin to "the east. At the close of the Paleozoic 

 this oceanic area, stretching as far eastward as the Wasatch, was lifted up 

 into a broad land-mass, and the former continental region sank below the 

 water and in turn l)e(;ame an ocean basin. Fi'om the Wasatch westward 

 to this ancient shore line the mountain ridges exhibit much in common in 

 their structural and physical features, being made up in great measure of 

 Paleozoic strata, whereas from this Ixmndary westward the ranges show 

 a, marked contrast in the nature; of their sedimentation and bear ample 

 paleontological evidence of their Mesozoic age. Over this latter area, not- 

 ably in the West Ilumlxddt, Piute, and Augusta Mountains, limestones 

 characteristic of the Triassic and Jurassic have been described in detail by 

 the geologists of the Fortieth Parallel I'^xploration," while to the east of this 

 shore line no Mesozoic rocks occur. Mr. King- assigns excellent reasons for 



'Geological Exploration of tlio Foiticlli I'.ir.ilNl. vol. i, Systeiiiiitic Geology, ]>. 733. WashiiiK- 

 toii: 1878. 



-Geologifal ExploratiDii <>( Die Foiliclh I'ar.illil, v.. I. ii. Dr.tiiiptivu Geology, \>]>. (i.'iT. 711, 

 and 724. Wasliington. 1877. 



