124 



GEOLOGY OF THE BLACK HILLS. 



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Minne Katta, Rapid, Spearfish, and Redwater. Some of the streams rise 

 again at intervals on the Plains, but none of them ever regain their original 

 volume. Such at least was their character at the time of our visit, but 



from numerous signs it would appear that in cer- 

 tain seasons or during great floods many or all of 

 them carry water in great volume to the Cheyenne. 

 This sinking of the water is no uncommon feature 

 in the western country, and it is due in many cases 

 to various circumstances of climate which need not 

 <£ be enumerated here. The sinking of the streams 

 « in the Hills takes place usually within a very small 

 g& area, and I surmise that it is caused by a down- 

 ward infiltration of the water into the limestones, 

 through which it has dissolved subterranean chan- 

 ^SnlM 5 i^|S nels, and from which it rises again at some distant 

 place. Sometimes, however, it may find a passage 

 under the visible bed of the stream among the 

 bowlders filling the channel, and from them it may 

 rise again in the Plains. Minne Katta, which in 

 the matter of sinking is an exception, issues from 

 a subterranean channel cut probably in the Car- 

 boniferous rocks; it rises in springs of great vol- 

 ume within a small area at the base of a cliff of 

 the upper Carboniferous series. 



Possibly after the work of active mining has 

 -2^1 been pursued in the valleys of the Hills for some 

 time, sending down the creeks large quantities of 

 fine sand and mud, some of them will become run- 

 ning streams out into the Plains, their old channels 

 of subterranean escape being filled up by the debris 

 carried down from the mining operations. 

 Returning- to the review of the Carboniferous rocks on the eastern side 

 of the Hills, on Rapid Creek is found one of the best exposures of the 

 sedimentary rocks that was anywhere examined. The creek runs for some 



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