ELK MOUNTAIN EEGIOK 149 



Measure limestone to the Fox Hill sandstone, uplifted at high angles, lying 

 against the Archaean foundation. All the geological divisions are well rep- 

 resented, in general exhibiting the same characteristics as seen elsewhere 

 in the Rocky Mountains, and only a few salient features require special 

 mention. Unlike the rigid beds east of the Colorado Range, which stand 

 out from the main mass in unbroken lines of strata, the beds at Elk 

 Mountain conform much more closely to the Archaean outline, and curve 

 around the older rocks lying directly upon the sloping sides. All the later 

 sedimentary strata are more or less disturbed, and show considerable 

 crumpling and local displacement. The Carboniferous limestones lie high 

 up on the mountain, in places reaching' within 1,200 or 1,500 feet of the 

 summit, and extend from the first canon east of Scotch Creek to the west 

 side of Sheep Butte. 



In the narrow caiion east of Scotch Creek, the limestones occur at the 

 entrance in a steep cliff, then, rising up over the gneisses, form a covering 

 200 or 300 feet in thickness, concealing the crystalline rocks beneath ; 

 both formations, however, being distinctly seen from the canon. These 

 limestones would appear to be much more arenaceous than the same beds 

 to the eastward. They all possess a coarse crystalline texture, more or 

 less sandy, many of the beds consisting largely of siliceous material of a 

 bluish-white color, interstratified with yellowish-white layers, and at the 

 same time are not so characteristically bedded as the Palaeozoic limestones 

 of the Laramie Hills. At Sheep Butte, the arenaceous habit of the lime- 

 stone is clearly shown. Here the beds stand at 80°, many of them almost 

 pure sandstones of a bluish-gray color. The Red Beds, Jurassic, and Da- 

 kota Cretaceous all occur on the slopes of the mountain, but much lower 

 down, and less regular in outline than the Carboniferous. East of Sheep 

 Butte, they all conform with the latter beds in following the deep re-enter- 

 ing bay in the Archaean mass, and then curving around the northern side 

 of the butte, completely encircling the projecting spur of Archaean rocks. 

 Just east of the summit of Rattlesnake Pass, the Dakota Cretaceous stands 

 out prominently, with its characteristic wall, above the softer Jurassic 

 marls on one side and the Colorado clays on the other, at an angle of 

 85°, striking north 75° to 80° east. From here eastward, nearly to Foote 



