peale-J EESUME PALEOZOIC EOCKS CAEBONIFEEOUS. 617 



represent a line of uplift "with a fault along its eastern side, could not be 

 positively determined. I am, however, inclined to believe the former, 

 and that they were islands in the Tertiary lake. 



Thompson Plateau. — This area of Carboniferous lies west of the two 

 island-like areas just described, and like them has westward-dipping 

 limestones. At the south end there may, however, be dips in the op- 

 posite direction. This plateau is directly on the line of elevation of 

 Meridian Eidge and the fine of the fold continuing northward from Piney 

 Creek. I am inclined to think there is faulting along the east edge of 

 the plateau, but it may be that this area only represents a higher portion 

 of the fold, in which erosion has been greater, so that the eastern side of 

 the anticlinal has been entirely removed. To determine which is the 

 correct view the southern end of the plateau will have to be more thor- 

 oughly investigated, and its connection with the Meridian Eidge deter- 

 mined. There may be a synclinal between the south end of the plateau 

 and Labarge Mountain. At the north end the Wahsatch beds come up 

 over the limestones. 



Wyoming Range. — This range continues northward from Piney Creek, 

 and is composed of limestones and a few bauds of quartzites, in which 

 no fossils older than Carboniferous were found by us. The eastern face 

 of the range presents a bluff of these limestones, which dip to the west- 

 ward at every point where this face of the range was seen. No detailed 

 section was made of the entire series in the range, but there must be a 

 thickness of from 5,000 to 6,000 feet of beds. Crossing the range from 

 east to west, we find the centre of the mountains occupied by a shallow 

 synclinal depression, which is best seen in the Triassic rocks north of 

 Station 55. On the western slopes, beds of the Jura-Trias outcrop, and 

 beyond them probable Cretaceous, all conformable to the Carboniferous. 

 This fixes the age of the mountains as Post-Cretaceous. Along the east 

 edge of the mountains the upper limestones of the bluff are from 2,000 

 to 3,000 feet above the sandstones that outcrop at the base. The latter 

 have been referred to the Laramie Group, and they dip to the west- 

 ward abutting against the westward-dipping Carboniferous. We have 

 here, therefore, an immense disrdacement, which exists along the entire 

 front of the range. The line of the fault is very irregular, curving to the 

 westward at a number of places so that bays of the more modern rocks 

 extend into the range. At first I thought the range was the shore line 

 against which these beds were deposited, but at no point along the range 

 did the Laramie sandstones show any evidence of their deposition in close 

 proximity to the shore line. The formation of this fault and the folding 

 observed east of the range and in its central portion were all probably 

 contemporaneous, and should be referred to early Tertiary time. When 

 the Wahsatch conglomerates were formed the Wyoming Eange formed 

 a part of the western shore of the lake. 



Salt River Range. — This, which is also mainly a Carboniferous range, 

 presents along its eastern face a fault like the fault of the Wyoming Eange, 

 with the downthrow also on the east. It was not accurately measured, 

 but it is fully as great in its extent. Its southern extension is perhaps 

 to be found in the fault along the east side of the Absaroka Eidge, which 

 is similar though not so great in amount. In the latter place tlie Fox 

 Hills Cretaceous abuts against the Carboniferous. 



The structure of the Salt Eiver Eange is so complicated that the 

 reader will have to refer to the detailed description in a preceding chap- 

 ter. Suffice it to say here that there - are a number of interesting folds 

 which at the southern end of the range involve the Jurassic and Cre- 

 taceous ! rocks as well as Carboniferous. The Carboniferous of the 



