524 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



morning snn slione on them and scattered tlie mist and smoke from their 

 summits, tliey seemed not far distant, and loomed up along the horizon 

 with a sharp, clear outline that rendered the view most grand and im- 

 posing. Fremont's and Snow Peaks were clearly defined, and the series 

 of sharp peaks that project from the main ridge seemed to diminish in 

 height far toward the sources of Green Eiver. In no country in the 

 world, it seems to me, can such a comprehensive view he presented to 

 the eye at a glance as at this point, where it can take in one of the loft- 

 iest of the ranges which form the main chain of the Eocky Mountains, 

 stretching along the horizon for at least one hundred and fifty miles." 

 Fremont, in his report, speaks in glowing terms of the Wind Eiver Mount- 

 ains, and compares the scenery to the finest in Europe. 



WIND RIVEE, MOUNTAINS. 



The Wind Eiver Mountains properly fall within the district assigned 

 the Sweetwater Division, and will be fuUj^ treated of in Dr. EndUch's 

 report. Still, as our division skirted the western foothills of the mount- 

 ains, there are several x)oints that ought to be referred to here. 



'Professor Comstock, on his geological map, has colored a series of 

 formations from the Potsdam sandstone to the Carboniferous, (Coal 

 Pleasures) inclusive, as outcropping on the west side of the mountains 

 between the head of the Big Sandj^ and Union Pass. As our party 

 skirted the edge of the mountains as far north as the heads of the New 

 Forks of the Green, we are prepared to say that in this distance the 

 Wahsatch Group of the Tertiary is superimposed to the granite, the 

 junction being frequently concealed by moraines. These latter will be 

 described by Dr. Endlich, who traced them from the mountains to the 

 basin. Outside of the foothills there are several granitic buttes, Fre- 

 mont's being the largest, whicli seem to have risen above the lake as 

 islands. 



The fact that the older formations do not outcrop on the southwest or 

 west side of the mountains was noted by Dr. Hayden in 1870. In the 

 report for that year he says : "I could not ascertain that any of the 

 older sedimentary rocks are exposed along the western side of this 

 range, from the South Pass to the sources of Green Eiver. Eidges of 

 the Lower Miocene Tertiary strata along the western limit of the meta- 

 morphic rocks form an immistakable shore-line of the ancient lake. 

 Between this shore-line and the foothills of the mountains is a belt of 

 metamorphic slates and gneiss, covered here and there with PUocene 

 marls." Our investigations confirm the absence of the older sedimentary 

 rocks. The Pliocene marls referred to do not extend as far as our dis- 

 trict. Dr. Endlich will treat of their occurreuce near South Pass. 



The shore-line of the ancient lake was undoubtedly granitic, as is shown 

 by the character of the deposits. The older formations probably occur 

 in the central portions of the basin, where they are concealed by the 

 Tertiary strata. The Wind Eiver Eange belongs to the same system as 

 the Front Eange of Colorado, and probably like it stood above the 

 level of the water in very early time. I have in other places indicated 

 my belief that the Eocky Mountains of Colorado were affected by a 

 subsidence extending through a long period of time, and I think it prob- 

 able that the Wind Eiver Eange partoolv of the same movement, and 

 that its jn^esent elevation is due to an elevation in Post-Cretaceous time. 

 Dr. Hayden was inclined to consider the Sweetwater Valley an extension 

 to the east or southeast of the axis of the Wind Eiver Eange. If so, it 



