144 



GEOLOGY OF THE BLACK HILLS. 



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Warren, the cone northeast of Inyan Kara, and Inyan Kara — it has been 

 bulged up at a high angle, and through it the igneous masses have been 

 extravasated. It does not encircle Crow Peak, but it marks out by its 

 flexure the limit in the Red Valley of the Crow Peak displacement. A 



long, low, rounded ridge, sheathed entirely by 

 the limestone, extends northward into the val- 

 ley a distance of three or four miles. The 

 thickness of the limestone is here from 15 to 

 25 feet. 



On the northwestern exposure it is cut 

 by the Redwater and its branches, some of 

 which run for miles in a westerly direction, 

 nearly coincident with the strike of the rocks. 

 One of the western branches heads in the Red 

 Beds southeast of Sun Dance Hills and enters 

 the purple limestone from a higher horizon, 

 while the main branch, rising in Floral Valley 

 on the Carboniferous plateau, enters the pur- 

 ple limestone from a lower horizon. The 

 lower red clay of the Red Beds is often in this 

 vicinity so sandy as to acquire some degree 

 of solidity. The upper red clay has a great 

 development, and gives to this part of the 

 Red Valley, as seen from an eminence, a 

 striking appearance not readily forgotten. 

 With a rounded, billowy surface, its blood- 

 red mass deeply gullied in all directions, 

 and with an occasional gash of white gyp- 

 sum exposed on the red field, the valley 

 stretches away to the dim line of the distant 

 rampart. 



Occasionally there is a small expanse of grassy surface, but the blades 

 are scattered and there is scarcely any turf. The only trees are a 

 few scattered groves that indicate the courses of the creeks. Notwith- 



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