HINTZE,, GEOLOGY OF WASATCH MOUNTAINS, UTAH 131 



thrusting, the weaker members in the lower part of the overthrust mass 

 having been rolled together in such a way as to make it almost hopeless 

 to try to make out any regular structures. Small Z-shaped folds have 

 resulted in several places, and in others, overturned and isoclinal folding 

 may be observed. North and south of Alta where the disturbance seems 

 to have been the greatest, the weak shales of the Cambrian system have 

 been drawn out into long tongues in the midst of the quartzites, entirely 

 isolated from the limestones which normally overlie them. The dynamics 

 by which this was accomplished in a i-egion so complicated can hardly be 

 explained. Tlie strata plainly show that they have been torn loose from 

 their normal position in the sedimentary series and involved in the zone 

 of shearing so as to be widely separated from their former position. 



In Big Cottonwood (^anyon, above the Alta black shale exposed near 

 tlie old Maxfield mine, rises a great series of limestones. Below the shale 

 is a thickness of about 1200 to 1500 feet of Cambrian quartzite, and 

 below that the Algonkian quartzite slate series 11,000 feet thick forms the 

 base of the section. There is thus in Big Cottonwood Canyon a great 

 limestone series overlying the Alta shale. These may both be traced south- 

 east across the canyon where the limestones are seen to form the top of 

 Kessler's Peak. Still farther along the strike, they cross South Fork and 

 are best seen as the chief rocks making up the Eeade and Benson ridge, 

 on the east wall of South Fork. They may be continuously followed 

 south into Little Cottonwood Canyon where they form the ore-bearing 

 zone north of Alta. The Cambrian black shale can be traced along in 

 the same way and some of the underlying quartzite, but just below Alta a 

 second lower series of limestones outcrops in bold cliffs on both sides of 

 the canyon, facing Superior and Peruvian gulches. To one familiar with 

 the Big Cottonwood succession where no limestones appear below the 

 Cambrian rocks, this condition at once suggests an overthrust. An ex- 

 amination of the rocks ]:»elow the lower limestone revealed the Cambrian 

 black shale as the first member and the familiar Lower Cambrian quartz- 

 ites and the upper part of the Algonkian quartzite and slate series as the 

 downward continuous succession. Below the upper limestones, which 

 were traced over from Big Cottonwood, are, in order going down, the 

 Cambrian black shale (Alta), the Lower Cambrian quartzite (Brigham) 

 and the upper part of the Algonkian series which rests upon the lower 

 limestones. There is thus a complete duplication of the strata from the 

 upper part of the Algonkian through the Cambrian and including the 

 lower 1000 feet of limestone of Ordovician and Devonian age. The evi- 

 dence for overthrusting is therefore conclusive from a stratigraphic view- 

 point. It seems strange that, the Fortieth Parallel geologists should 



