HEAD OP BLACK'S FORK. 255 



plateau (Concrete Plateau), capped by beds of the Wyoming Conglomerate. 

 At Ijime Pass, the denudation of these beds has exposed the limestones 

 of the Upper Coal-Measures, dipping 45° to the northward, and striking 

 about 15° north of east. The better exposures are heavy, massive beds of 

 grayish-blue limestone, which stand out in ridges, while the upper and more 

 argillaceous beds have been worn away into low saddles and ravines, and 

 covered up by surface accumulations and vegetation. On the eastern side 

 oi the west branch of Black's Fork, opposite Lime Pass, these softer beds 

 are seen to consist of mud-rocks and slates, which' probably correspond to 

 the Permo-Carboniferous beds of this character in the Weber Canon, while 

 in the limestones were found a few Carboniferous fossils, among which only 

 a Productus Prattenianus has been specifically determined. Overlying the 

 slates and mud-rocks were found coarse-gray and reddish sandstones of 

 the Triassic formation, whose exposures as observed were too limited to 

 afford a continuous section of the formation. Doubtless, a more detailed 

 examination might disclose also outcrops of some of the higher formations, 

 which were hidden by the forest-covering from the general examination 

 made by us. The lower beds of the Upper Coal-Measure group consist 

 here of conglomerates, which, on the western side of the valley, are 

 very coarse, while on the eastern ridge they have more the character 

 of a coarse-grained gray sandstone, made up of grains of limpid quartz in 

 a siliceous matrix, and sometimes stained by iron oxide. 



A great thickness of the underlying beds of the Weber Quartzite 

 group is exposed in section by the can on- cutting of the upper valley 

 of the west branch of Black's Fork. In the narrow ridge between 

 the head of Black's Fork and Bear River, the dip gradually steepens 

 from Lime Pass upward, from 45° to 52°, without showing any non-con- 

 formity, and toward the head of the ridge shallows again to 16°, beyond 

 which, in the axis, there seems to be a sudden break, and in the peaks near 

 the head of the canon the beds dip 5° to the southward. The upper beds 

 of this group (the Weber Quartzite) here consist mainly of coarse red sand- 

 stones, frequently characterized by a fine striping parallel to the bedding- 

 planes. Below these is a great thickness of red and purple quartzites, made 

 up of rounded grains of quartz, sometimes so large as to constitute a fine con- 



