414 DESCRIPTIVE GEOLOGY. 



vertical position, that is, at right angles to the bedding-planes of the 

 rock. 



On the Cambrian plateau, south of the Blacksmith's Fork, extending to 

 the divide between the Muddy and Beaver Creek, occur isolated patches of 

 Tertiary sandstone. The largest body is some 4 or 5 miles in length, 

 lying between two branches of the Blacksmith's Fork, and rising about 500 

 feet above the level of the quartzite. Other smaller beds are found along 

 the western base of the Bear River Plateau, which conceal the line of junc- 

 tion between the quartzite and the overlying limestone, forming frequently 

 low hills or mounds, and stretching up the slope of the ridge for 200 or 300 

 feet. The same formation may be traced in small remnants over a consid- 

 erable part of the plateau, within the designated area, although to the north 

 of Blacksmith's Fork it was not recognized. These Tertiary beds have been 

 referred to the Vermillion Creek series, partly from their close lithological 

 resemblance, and partly from their apparent relation with the Tertiary series 

 of the Bear River Plateau, although it is proper to state that no direct con- 

 nection between these two formations was traced, and they may possibly 

 be of later age. They generally consist of a coarse, sandy rock of loose, 

 friable texture, colored bright red from the presence of a considerable 

 amount of oxide of iron. 



The easterly-dipping beds of the Cambrian pass under the Bear 

 River Plateau, and are concealed beneath the overlying beds of lime- 

 stone. The arenaceous and argillaceous slates, which are so well shown 

 on the western side of the axis in Muddy Canon, were nowhere observed on 

 the eastern fold; the line of contact between the Cambrian and Silurian 

 being very much obscured by remnants of Tertiary beds, and considerable 

 accumulations of Quaternary detrital material, brought down from the pla- 

 teau above. 



Bear River Plateau extends for nearly 25 miles in an unbroken line 

 from the northern limit of the map, rising 2,000 to 2,500 feet above the 

 Cambrian summit. All along its western face, there is exhibited an abrupt 

 precipitous wall, cut by a few deep canons, whose streams are branches of 

 Blacksmith's and the Muddy Fork. These canons, or rather gorges, are 

 very narrow, and cut -deeply into the limestone down to the underlying 



