146 jS. F. Emmons — Little Cottonwood Granite. 



Oquirrh and Wasatch Mountains there has been the greatest 

 concentration of ore deposits. This generalization holds good 

 at the present day, but modern developments show that there 

 is an evident genetic connection with the older eruptives, while 

 none is apparent with the extrusive flows. 



The further statement in my original report,"^ that in the 

 Wasatch range the mineral de])osits are mostly concentrated 

 wdthin a radius of 6 or 7 miles around Clayton Peak, also holds 

 good in the light of present developments, which, moreover, 

 point to a more intimate genetic relation of ore deposition to 

 the Clayton Peak than to the Cottonwood body, for as far as 

 known no ore deposits have been found on the contact of the 

 latter with the surrounding rocks, whereas they are most com- 

 mon around the Clayton Peak mass. It must be noted, how- 

 ever, that these deposits occur for the most part in calcareous 

 rocks, and no calcareous rocks are known to occur in contact 

 with the Cottonwood granite. It may be assumed that the 

 Cottonwood granite, if regarded as a distinct body, did not reach 

 a higher horizon than a thousand feet or more below the top 

 of the Cambrian quartzite. That the Cottonwood and Clayton 

 Peak granite beds were part of the same mass and hence of 

 contemporaneous origin, was a plausible assumption as made by 

 the 40th Parallel geologists but one which has not yet been 

 supported by the finding of any connection between the two 

 on the surface. In the absence of such connection a possible 

 alternative hypothesis is that there have been successive erup- 

 tions in this region from the same general magma, each of 

 which reached a higher geological horizon than the preceding 

 one. On this hypothesis it may be assumed that the Cottonwood 

 batholith was intruded while the Cambrian beds were still rest- 

 ing undisturbed upon the upturned edges of the Archean, and 

 that it did not reach the top of the Cambrian ; that this erup- 

 tion was followed later by the mountain-building movement 

 which threw the Paleozoic beds into anticlinal and synclinal 

 folds, and that after they were thus upturned, the Clayton 

 Peak mass intruded into the Carboniferous limestone and pro- 

 duced the well recognized contact phenomena now seen. The 

 stocks or dikes of porphyry in the somewhat higher geological 

 horizons to the eastward might have been contemporaneous or 

 slightl}^ later eruptions from the same general magma, and have 

 owed their less completely crystalline structure to the differing 

 conditions under which tliey consolidated. The abundant 

 mineralization in the region has evidently been in part a direct' 

 and in part an indirect result of this phase of activity. 



As regards the extrusive flows in the depression between the 

 Wasatch and Uinta Mountains, they rest on a surface from 



*Ibid, p. 864. 



