PBALE] RIESUM]^ — ARCH^AN — PALEOZOIC. 613 



AECHJEAI^ EOCKS. 



The Archaean rocks of our district are limited to the extreme north- 

 east corner of the area where the foot-hills of the Wind Eiver Mount- 

 ains and a few isolated buttes are composed of a granite which is made 

 up of a red feldspar and gray quartz and muscovite. These buttes 

 appear to have been islands in the earlier Tertiary lakes. As the 

 main mass of the mountains is within the limits of Dr. Endlich's dis- 

 trict, I shall leave the discussion of these rocks to him. Thej' uader- 

 lie the soft beds of the Wahsatch Group, the lowest layers of which 

 are evidently derived from the degradation of the granitic rocks. 

 There is a slight inclination from the hills as though there had been 

 some elevation of the Wind Eiver Mountains subsequent to the dep- 

 osition of the Tertiaries. The angle of inclination is greater than 

 would be expected if the strata were merely deposited on a sloping bed. 

 The mountains formed the shore of the lake all through Tertiary time, and 

 probably towered above the Palaeozoic seas from early time, as did the , 

 Eocky Mountains of Colorado, with which they were probably synchro- 

 nous. There was probably also a contemi^orary subsidence. At any 

 rate, the evidence appears to point to a subsidence of the range and that 

 of the Green Eiver Basin during Tertiary time. On the west side of 

 the basin the Wahsatch beds rest unconformably on Jurassic and Cre- 

 taceous strata that were crumpled and folded jDrior to the existence of 

 the later Tertiary Lakes. These older beds terminate to the eastn^jard 

 beneath the Wahsatch Group somewhere between the Wind Eiver Eange 

 and the west side of the basin. The most prominent of the isolated gran- 

 itic areas near the Wind Eiver Mountains is rr6mont's Butte. It is on 

 the south side of Willow Creek, and rises 650 feet above the creek level. 



In the preceding chai^ter I have referred to the fact of Mr. Hague 

 finding granitic boulders in Logan CaSon. If there is a granitic area 

 at the head of either of tlie forks of Logan Eiver it must be very lim- 

 ited in its extent, probably appearing only at the bottom of the canons. 

 None were seen by us, and I merely mention the probability of the 

 occurrence. 



PALEOZOIC EOCKS. 



At no point within the district was I able to obtain a continuous sec- 

 tion from the base of the Palaeozoic to the top. In the east, the lowest 

 Palaeozoic outcrops identified are Carboniferous, and in the west the 

 Cambrian rocks are the lowest and show by the erosion of the overlying 

 beds; but at no place could I get an uninterrupted section from the 

 lo^^est exposure of the Cambrian to even the top of the Silurian. The 

 general section given is comjjiled from the various outcrops, which are, 

 however, sufficiently connected to show that the entire section is con- 

 formable. It is i)ossible that a portion of the baise of the Carboniferous 

 section as given in this report in the Wyoming and Salt Eiver Eanges 

 should be referred to the Devonian. In the absence of fossils other 

 than Carboniferous I have included it with the Carboniferous. 



In the Bear Eiver Eange, Devonian occurs according to the state- 

 ments in reports of the fortieth parallel survey. We found no fossils, how- 

 ever, and, even if found, our exaudnations were not detailed enough to 

 carry the subdivisions over the whole district, and I have not, therefore, 

 separated the Devonian, in this western portion of the district, from the 

 Carboniferous. 



SILURIAN". 



The recognized Silurian areas of our district all lie- in the west half. 

 The most eastern exposures were noted in the Bear Eiver Eange, but 



