THE FORTIETH PARALLEL SURVEY. 



605 



I III 



iferousj and Nevada Devonian Between Little Cottonwood and Amer- 

 ican Fork .... all these beds standing at higk and varying angles, and being 

 ranch broken and contorted." 



In Volume I. Mi*. King remarks (pp. 44-48) ; 



" The Archaean rocks in the explored portions of the Wahsatch are exposed 

 at -intervals along the weat front of the range for nearly 100 miles, and are 

 composed of granites, garnet rocks, aplitic schists, and a very extended seiies 

 of gneisses and hornblendic schists, with subordinate quartzites. The man- 

 ner of their exposure is of very great interest, involving the most extensive 

 dynamic action observed within the limits of the Fortieth Parallel Exploration. 

 The chain of out-crops clearly represents an old Archa3an range of bold con- 

 figuration, which has been buried beneath an enormous accumulation of 

 Pala3ozoic and Mesozoic sediments. It was this buried Archaean range which 

 controlled tlie position and direction of the modern Wahsatch Range. After 

 the uplifts took place, and the Palaeozoic and Mesozoic strata were thrown into 

 their present inclined position, a great longitudinal fault occurred throughout 

 thiis whole portion of the range, by which the entire western half of the ridge 

 was thrown downward from 3,000 to 40,000 feet, and is now entirely buried 

 beneath the Pliocene and Quarternary formations of the Salt Lake basin. The 

 present abrupt west front of the Wahsatch is the standing face of this great 

 fault, and here the Archaean rocks are seen to occupy the core of the range, 

 unconformably underlying the Palaiozoic series, and rising to different strati- 

 graphical horizons in the overlying series. In the southern portions of Map 

 III., in the region of Cottonwood and Little Cottonwood caiions, is exposed an 

 approximately conformable series of 30,000 feet of Palaeozoic strata, overlying 

 the granite and schists which there together form a portion of the, early 

 Archaian surface. The origin and nature of the granites at this point are 

 obscure. There seem to be two distinct types — a granitoid gneiss, having a 

 decMed stratification, and an apparently eruptive body, which possesses in an 

 interesting degree the conoidal structure so prominently developed in the 

 granites of the Sierra Nevada. About fifteen miles south of Salt Lake City 

 the Palseozoic beds are thrown into a broad semicircular curve, having a con- 

 vexity to the east and a varying dip always away from the centre of this curva- 

 ture. The ends of the strata of this great flexure advance westward until they 

 approach the region of the great fault, their eroded edges forming the foot-hills 

 of the range. The centre and nucleus of this immense curvature is a body of 

 Archtean rock, composed partly of schists, but principally of a great central 

 mass of granite and granitoid gneiss, having its best exposures in Little Cot- 

 tonwood Canon and the peaks to the south, and again in the Clayton's Peak 

 mass, where it rises like an island through the strata of the Lower Coal Meas- 

 ure limestone and the Weber quartzite Although in Clayton's Peak, 



and again near the lower end of Little Cottonwood Canon, the rock possesses 

 all the physical habit of a truly eruptive granite, and although in the Clayton's 

 Peak region the granite has undoubtedly been a centre of local metamorphisui 



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