128 ANNALS NEW YORK ACADEMY OF SCIENCES 



quaquaversally from the nucleus of granite, this great series of sediments 

 forms the eastern half of a huge dome abruptly cut off on the west by a 

 profound fault. The western half was depressed and is now entirely 

 covered by the deep accumulation of rock waste forming the floor of the 

 Salt Lake Valley. Eastward, the Carboniferous and Triassic formations 

 are breached by an irregular stock of fine-grained granodiorite which 

 culminates in Clayton Peak. Beyond this line of elevation, which forms 

 the present divide, an extensive flow of andesite was poured out in an 

 elongated synclinal depression that separates the Wasatch from the 

 western Uintas. It is significant that the anticlinal fold of the Uinta 

 range is in line with the eastward prolongation of this domed arch and 

 that they are connected beneath the igneous covering by the Kamas 

 prairie syncline. 



Little Cottonwood Granite 



The structural relation of the Little Cottonwood granite to the sedi- 

 ments which flank it upon all sides has been variously interpreted. By 

 the geologists of the Fortieth Parallel, the contact was described as one 

 of sedimentary unconformity; and the granite was thought to be older 

 than the quartzites that appear to overlap it. The absence of a basal 

 conglomerate was noted, and the whole situation was thought to be ex- 

 traordinary. At that time, the intrusive occurrence of granite had not 

 been conceived, and the indications of contact and regional metamorphism 

 escaped notice, so that while the evidence of a sedimentary contact was 

 not in accord with conditions commonly regarded as necessary, the rela- 

 tion was still held to be due to sedimentation. 



In 1880, Geikie^* visited this region and later published his conclu- 

 sions. He found structural evidence that led him to regard the granite 

 as intrusive, and probably post-Carboniferous in age, rather than pre- 

 Cambrian as given by the Fortieth Parallel geologists. 



In 1900, Boutwell visited Little Cottonwood Canyon and examined 

 the contact of the granite and quartzite on the ridge south of Twin 

 Peaks. Here he found dikes of granite extending up into the quartzite 

 and sills of granite leading off laterally from the dikes. Inclusions of 

 quartzite in the granite were also observed, and the intrusive nature of 

 the granite was thus established. These results were verifled by Em- 

 mons^^ who later published his conclusions regarding the granite as in- 



•'^ A. Geikie: "Archean Kocks of Wasatch Mountains," Am. Jour. Scl., 3rd Ser., Vol. 

 19, pp. 363-367. 1880. 



35 S. F. Emmons: "Little Cottonwood Granite Body of the Wasatch Mountains," Am. 

 Jour. Sci., 4th Ser., Vol. 16, pp. 139-147. 1903. 



