142 



GEOLOGY OF THE BLACK HILLS. 



Jura. 



Feet. 

 5. Sandstone, red or pink, soft at bottom and bard at top, witb numerous ripple 



marks 8 



4. Sandstone, yellowisb and greenisb, witb some tinge 

 of red ; containing some calcareous matter in 



co tbin bands 10 



3. Wbite sandstone 3 



12 



pq 



Bed Beds. 



2. Deep red clay 



1. Gypsum to bed of creek . 



50 



8 



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43 



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From Amphibious Creek to Burnt wood the 

 Cretaceous rampart is very prominent, and near the 

 pass of the latter, called "Buffalo Gap," it culmi- 

 B „ d | s nates in high hills. On French Creek, though the 

 entire Red Bed series is exposed in places, its struc- 

 ture is not well developed, and the Red Valley is 

 but poorly marked. 



From Battle Creek northward past Rapid, Box 

 Elder, and Elk Creeks, the Red Valley has again a 

 fine development, extending to and joining the east- 

 ern extension of the great Redwater Valley on the 

 north side of the Hills, and having a width, includ- 

 ing the outer slope of the purple limestone, of 

 from two to six miles. The profile and cross- 

 section are nearly the same as on Amphibious 

 Creek (Fig. 20). North of Rapid Creek the lime- 

 stone warps up and creates a ridge in the center of 

 the Red Valley, as shown in the accompanying 

 figure (21). If the uplift be disregarded, an idea 

 may be derived from the diagram of the general 

 structure of the Red Valley on the eastern side of 

 the Hills. 



The purple limestone is very prominent on the eastern side of the 

 Hills. Along the entire margin it forms a gentle slope, rising from the red 



6 



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