70 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



tliose veins is simply iron (liematite), witli a trace of silver. This cliar- 

 acter alone indicates a difference between the formations containing the 

 veins. Following ont the lesson tanght by the character of these occnr- 

 rences, we may conclude that the main chain of the Wind Eiver Eange 

 will not be found to contain auriferous lodes. They will be confined 

 almost entirely to the old metamorphic schists. 



The total area covered by the metamorphic rocks is quite an extensive 

 one. Beginning near the northwestern corner of our district their bor- 

 der runs along the w^estern base of the Wind Eiver Eange near the point 

 where the Sweetwater issues from the mountains ; the metamorphics 

 make a curve to the southward, reaching Pacific Springs. From there 

 they turn toward the eastward, and end at the Little Caiion of tlie Sweet- 

 water. Curving northward, and afterward to the northwest, they re- 

 main inside of the third chain, following a course approximately par- 

 allel Avith the trend of the range. 



Isolated outcrops occur south of Sheep Mountain. A number of hills 

 are found there, having a general trend south of east, which are com- 

 posed of granite. It is the same rock which we have heretofore found 

 along the base of the foot-hills. These granitic outcrops disappear, in. 

 part, under the younger Tertiary strata to the southward ; in part they 

 are covered by the reel sandstone we find at the base of the foot-hills. 



Either the force which caused the elevation of the Wind Eiver Eange 

 had spent itself near this point, or the same class of material which com- 

 poses the greater portion of the range did not exist here. I am inclined 

 to this latter view. We have, as wiU be seen subsequently, ample evi- 

 dence in this region of severe disturbances, but we nowhere^ find either 

 the schists of the eastern slope or the granites of the main chain. The 

 granites here totally disappear from sight, and are not found again until 

 they crop out in the Siveetwater Mountains. While this granite once 

 more shows itself, the schists of the Camp Stambaugh region do not 

 again appear on the surface. During the discussion of the Sweetwater 

 area we shall have occasion to enter into these features more fully, as we 

 there find the continuation of several imi)ortant groups. 



PALEOZOIC FOEMATIONS. 



SILURIAN. 



Groups of the Silurian formation have been found, with some inter- 

 ruptions, aU along the eastern base of the Eocky Mountains. Usually 

 they are limited to the Potsdam and Calciferous series. In Southern Col- 

 orado, strata have been found at Canyon City, Colorado Springs, and far- 

 ther north, at the eastern base of the Front Eange, which belong to these 

 groups. From there north and northwest a number of localities have 

 been observed where they occurred. We find in our district a discon- 

 nected series of Silurian strata. 



Fotsdam Crroup. 



On the eastern base of Wind Eiver Eange we observe a hard, red, 

 quartzitic sandstone directly overlying the youngest metamorphic gran- 

 ites. Extending upward on the gently-slopmg ridges at the eastern edge 

 of the second chain, these quartzites occupy positions rendering them 

 X)rominent and of importance in the landscape. Cut away by erosive 

 action they recede eastward in the narrow valleys and canons, but reach 

 up for various distances on the ridges intervening. Thus a horizontal 



