hsdiich.] SWEETWATER VALLEY CARBONIFEROUS. 103 



preserved corals were noticed in the dolomites and magnesian limestones. 

 The great strains to which these members of the Silurian formation have 

 been subjected hare resulted in numerous joints and fractures. This 

 feature is particularly noticeable in the quartzites, which weather in 

 sharp, angular bowlders. 



CARBONIFEROUS. 



Subcarboniferous. 



Occupying the same relative position as it does farther to the north- 

 west, we* find the Subcarboniferous strata within the region of the Sweet- 

 water drainage. Composed of the same beds here as there, they are 

 found underlying the massive blue limestones of the Carboniferous 

 Group. Near the Little Canon of the Sweetwater the dolomites and 

 sandstones belonging to the group overlie the Potsdam sandstones. A 

 large portion of them are hidden by the Tertiary beds, which there occupy 

 disconnected areas. At the western end of the Sweetwater Hills the 

 dolomites mostly rest directly upon the Prozoic granites, dipping, gen- 

 erally, to the northward and northeast. They are covered by the Car- 

 boniferous series, which, in turn, is hidden from sight by the overlying 

 Tertiary beds. In the Sweetwater and Seminole Hills, as well as directly 

 west of the Granite Hills, the Subcarboniferous Group is thoroughly con- 

 formable with the Silurian. Its thickness may be estimated as varying 

 from 700 to 900 feet, increasing toward the east. Very few fossils were 

 found, all of them in an exceedingly poor state of preservation. 



Carboniferous Group. 



In the region of the Sweetwater the Carboniferous Group becomes of 

 considerable importance. Appearing first in connection with the Silu- 

 rian beds near the Little Canon, the blue limestones are covered to the 

 southward by Tertiary deposits. They are again exposed in the area of 

 the granitic hills south of the river. Occupying either the slopes of these 

 hills or forming ridges which trend about X. 45° W., they dip toward 

 the north and northeast. Nothing further is seen of them until we reach 

 the western end of the Granite Hills. At the northern edge of the 

 plateau we find some very interesting outcrops. We see there the effects 

 of the termination of an anticlinal upheaval. It is essentially one of 

 that character which Dr. Hayden regards as typical for the entire region. 

 They occur in Dakota, Wyoming, and adjacent Territories. By the up- 

 heaval an arrangement of strata has been produced which forms an oval 

 or long-drawn quaquaversal fold. In this instance the Subcarboniferous 

 strata are the lowest ones exposed, as the presence of the Granite Hills 

 probably prevented the carrying up of older strata. By this same up- 

 heaval the younger granites to the northwest of the Prozoics have been 

 raised, but not sufficiently high to produce a rupture of the Carboniferous 

 beds sufficiently great to let the Silurian strata appear. Two sections 

 (X and XI) will illustrate the conditions here existing. The first one 

 runs approximately north and south, the second east and west. 



Beginning at the southern end of Section X we find the Tertiary beds 

 (i) overlying Carboniferous (d). In this line we cut the point on the 

 Sweetwater, where it flows through a narrow gorge of Silurian and Car- 

 boniferous strata. This is located near the continuation of the anticlinal 

 fold which in previous sections has been marked A. North of the river 

 the limestones dip at an angle of 15°. They are soon covered again by 

 Tertiary strata, but reappear, dipping southward 8°. The obscured 



