142 S. F. Emmons — Little Cottonwood Granite. 



Cambrian topography must have been of far bolder type than 

 that of the present day, the existence of this 30,000 foot cliff 

 has been regarded by geologists with some incredulity. 



As tJie result of a brief personal visit to the region. Professor 

 (now Sir) Archibald Geikie published a criticism"^ of Mr. King's 

 views, based largely upon improbability of the existence of a 

 cliff of such enormous dimensions, and concludes that the 

 intrusion must be of post-Carboniferous age. Later in his 

 text-book of geology he quotes this occurrence as " shown to 

 be of post-Carboniferous age."t 



A reply to Professor Geikie's criticism, on the part of Mr. 

 King and myself, has awaited the opportunity of making a 

 further study of the region which should be conducted with 

 suflSciently greater thoroughness than either of the previous 

 examinations to settle the question once for all. In conse- 

 quence, however, of the extreme ruggedness of the region and 

 the difficulty of access by most of the contact lines, lying as 

 they do along the edges of precipitous mountain summits, such 

 an examination would require several weeks' work with a 

 camping party and the opportunity of making it has hitherto 

 not presented itself. In Chapter YI of my report on the 

 " Geology of Leadville," however, in discussing the extent of 

 the absorbability of sedimentary rocks by eruptive masses, I took 

 occasion to refer to one of the arguments that had influenced 

 us in arriving at the conclusion that the Little Cottonwood 

 granite was pre-Cambrian. This was, briefly, that the other 

 assumption, namely, that it w^as later than the Cambrian quartz- 

 ites that rested upon it, involved the absorption of some 500 

 cubic miles of these quartzites by the intrusive magma which 

 ought to have resulted in making the magma unusually acid, 

 whereas in point of fact, the Cottonwood granite has only 

 71*78 per cent of silica, which is but normal and not a specially 

 acid type. I also referred to the fact that no included frag- 

 ments of Cambrian quartzites had thus far been found in 

 granite, although along the Archean contact, near the mouth 

 of the canyon, such included fragments are of frequent occur- 

 rence. On the other hand, I did not mention the fact that 

 occasional pebbles of granite had been found in the quartzite, 

 for the reason that we had not yet observed marginal zones of 

 basal conglonierates, such as Professor Geikie very justly 

 observed ought to be found at the base of such slopes of land. 



Yan Hise:f examined the canyon in 1889 and found granite 

 pebbles in the Cambrian quartzite which he, however, regarded 

 as lithologically unlike the Cottonwood granite. He con- 

 sidered the Cottonwood and Clayton Peak granites as identical 



*This Journal (3) xi, p. 363. f Edition of 1882, p. 646. 



tU. S. Geological Survey, Bull. 86, p. 294, 297. 



