144 S. F. Emmons — Little Cottonwood Granite. 



The outcrop of the Clayton Peak body occupies the divide 

 between the heads of Little and Big Cottonwood canyons, the 

 basin at the head of the latter canyon, and the mass of Clayton 

 Peak wliich forms its eastern rim ; it also extends for some 

 distance east of the latter peak in the plateau-like basin at the 

 head of Little Snake Piver, where its outcrops are obscured by 

 surface accumulation. 



In my original visit to the head of Big Cottonwood Canyon, 

 in 1869, I collected a specimen of crystalline garnet rock 

 which presented something of a schistose structure and was 

 thought to belong to the Archean complex. At that time the 

 results of the studies of contact metamorphism by Doelter and 

 others in the Predazzo-Thal and other classic localities in 

 Europe had not been published, and even to Prof. Zirkel, who 

 examined the specimen microscopically, the suggestion did not 

 present itself that this was probably a phase of contact altera- 

 tion of limestone. At the present day, however, when the 

 original dense forest-covering has been cleared away and pros- 

 pectors have sunk holes wherever the contact of limestone and 

 granite is exposed, these contacts are readily observed and 

 show conclusive evidence of the later intrusion of the granite 

 into limestone in the abundant development of contact min- 

 erals, such as vesuvianite, garnet, etc., and of contact deposits 

 of ores of the metals, in which the association of magnetite 

 with pyrite, chalcopyrite, galena, etc., is most common. Mar- 

 morization of the limestone is abundant in the region and by 

 no means confined to the contact belt, but, as Mr. King 

 observes, spreads out over large areas in the limestone beds 

 that have no definite relation to any known outcrop of erup- 

 tive rock. 



The prevailing rock of the Clayton Peak rock is a granular 

 diorite of the same general mineralogical composition as the 

 Cottonwood granite, but of finer grain and apparently carrying 

 less quartz and a greater proportion of basic silicates. The 

 western portion of this body on the divide between Big and 

 Little Cottonwood canyons, however, is of somewhat coarser 

 grain and resembles the granodiorites of the Sierra Nevada. 

 A small body exposed in Big Cottonwood Canyon, about two 

 miles below the bend and in the same general geological 

 horizon as the Clayton Peak mass, but some four miles north 

 of the outcrop of the Cottonwood granite, is of the fine-grained 

 dioritic type characteristic of the Clayton Peak mass. 



Each of the diorite body of the Clayton Peak, the eastern 

 spurs of the Wasatch Mountains, are made up of Paleozoic 

 beds cut through quite irregularly by stocks and dikes of erup- 

 tive rocks of distinctly porphyritic structure, though of the 



