MEDICINE BOW BANGE. 107 



when the rock, of course, is much whiter; in other beds, it is finer-grained, 

 but still made up of sharp angular pieces of siliceous minerals. It is de- 

 scribed thus somewhat in detail, as in many respects it bears a close 

 resemblance to what have been called the Red Jasper Conglomerates of 

 the Huronian series, as observed in the region bordering the north shore 

 of Lake Huron, by the Geological Survey of Canada.^ These red beds 

 of the Medicine Bow Range, however, are not over 500 or 600 feet in 

 thickness. They are overlaid by a thin formation of fine crystalline, almost 

 amorphous quartzite, of a bluish-gray color, and traversed by seams of 

 translucent quartz. The rock resembles the narrow siliceous belts inter- 

 stratified in the Triassic, Star Peak limestone of "Western Nevada. The 

 interstices and cracks in the quartzite are everywhere filled with carbonate 

 of lime. Thin sections, examined under the microscope, show minute calcite 

 particles disseminated through the rock in a manner, as Professor Zirkel 

 has pointed out, that is exceedingly rare in highly crystalline quartzites. 



The top of the peak is capped by patches of light gray and white 

 siliceous linfestone, that have escaped erosion. In texture and general 

 habit, it resembles the underlying quartzite, and seems only to have 

 passed from a prevailing siliceous bed to one of a calcareous nature. 

 Weathering has produced very characteristic outlines, and the exposed 

 surfaces are usually very rough from a confused net-work of minute ridges, 

 formed by the preservation of red siliceous seams, while the surrounding 

 limestone has been carried ofi*, producing, when seen in the field, a most 

 singular efi'ect. 



But little opportunity was afforded for an examination north of Mill 

 Peak of the higher portions of the eastern ridge of the Medicine Bow 

 Range, and it was therefore impossible to trace northward the white and 

 ferruginous quartzites and limestone. For 10 or 15 miles along the foot- 

 hills, and for long distances up Rock Creek, Cooper Creek, and the other 

 large canons, heavy dark schists and gneisses prevail. They all appear 

 to be more or less distinctly bedded, with the same general lithological 

 habit and forms of erosion as mark the rocks of the east side of the Platte 

 Valley. South of the Little Laramie River, in the region of Bellevue Peak, 



'Geological Survey of Canada, ISfiS, 57. 



