endlich.] SWEETWATER VALLEY PALAEOZOIC. 101 



occupying but a small area on the side of the Mils. By the protrusion 

 of this newly-appearing granite, the beds have been very much dis- 

 turbed, and in several instances directly doubled up. I regard this 

 phenomenon as due to the influence of the anticlinal upheaval desig- 

 nated as B. Throughout the Sweetwater Valley no evidence can be 

 found of it except near the western border of the Granite Hills. Pos- 

 sibly this upheaval has nothing to do with the occurrence, but in this 

 case its peculiarity could only be explained by the acceptation of an 

 independent elevation along a line parallel with the trend of the hills. 



Following along the summit of the hills, we find that nearly all of the 

 northern slope is obscured by Tertiary strata and drift. Granite contin- 

 ues to form the central mass. On the south side younger sedimentary 

 strata dip off from the granites. At Whiskey Gap the connection be- 

 tween the latter is entirely broken. 



The granite of the Sweetwater Hills comes to an abrupt termination, 

 and the succeeding range shows its highest points occupied by sedimen- 

 tary beds. At this locality the disturbing granite (c) evidently makes 

 a subterranean curve, but appears again a short distance east of the 

 gap. This condition of structure is illustrated by section IX. 



We find the granitic area gradually widening as we go eastward, 

 pushing the sedimentary beds toward the southeast. Dipping steeply 

 at first to the south, they gradually assume a more gentle inclination. 

 Bed follows bed until the younger Cretaceous strata are reached, which 

 eventually form the low country extending toward Fort Steele. 



In no instance do the sedimentary beds appear with a northward slope 

 on the north side of the granites. It might be supposed that they were 

 elevated and pushed beyond the vertical, but the order of the beds 

 would in that case necessarily be inverted. We have evidence at a 

 number of points that the Sweetwater Group covers older sedimentary 

 strata reaching down to the Silurian, and I am inclined to ascribe the 

 absence of such groups on the north slopes of the hills to the effects of 

 early erosion. When the maps shall be completed I will be able to pre- 

 sent horizontal sketches of the former and present of this region which 

 region which will make clear the dynamic actions involved. At first 

 sight they appear complicated, but they can readily be reduced to a 

 comparatively simple system. 



PALEOZOIC FORMATIONS. 



SILURIAN. 



At a number of localities within the Sweetwater drainage we find 

 Silurian strata. In part they are a direct continuation from the region 

 farther northwest ; in parts they appear after having been hidden for 

 some distance by supermcunibent strata. 



Potsdam sandstone. 



A good exposure of the red quartzites belonging to this group is found 

 near the Little Caiion of the Sweetwater. The wagon-road leading to 

 Stambaugh crosses the upturned strata. In accordance with the posi- 

 tion and configuration of the schists upon which they rest, the quartzites 

 show an easterly dip amounting to about 30°. They form a portion 

 of the canon walls. Trending in a southeasterly direction, they are 

 soon lost, however, within the Prozoic Group at the western end of 

 the Sweetwater Hills. I do not recognize them with certainty. Going 



