126 BULLETIN OF THE 



suited for a monograph, and thus it was that Newton discussed 

 them. 



The general form of the group was exhibited by an illustration 

 conveying the appearance they might present to the eye of an 

 observer elevated many miles above the extreme southern end. 

 The sedimentary rocks from the Potsdam sandstone up to the sum- 

 mit of the Cretaceous, are flexed upwards towards the hills from all 

 directions. Upon the western side, the Carboniferous strata after 

 being flexed upward, flex back to approximate horizontality upon 

 the summit of the uplift, while later beds are cut off and expose in 

 succession their upturned edges upon the flanks of the hill region. 

 The eastern part of the uplift is denuded of even its palseozoic 

 beds, and exposes a mass of contorted Archasan schists. 



The drainage of the entire area is collected into two streams, the 

 Belle Fourche and the North Fork of the Cheyenne. These 

 streams cross the south and north extensions respectively of the 

 Black Hills uplift, cutting profound valleys in so doing. The trib- 

 utaries of these streams all head around a central axis in the 

 western or plateau part of the region, and flow thence in all direc- 

 tions, gradually gathering into the two forks. It now becomes of in- 

 terest to inquire how far the positions and courses of these streams 

 have been dependent upon the deformations which the strata have 

 undergone, and how far upon antecedent causes. With this view, 

 streams may be considered as belonging to two classes — 1st. Conse- 

 quent streams, which result from the formation of the slopes down 

 which they run, and have had their courses determined by such 

 slopes. 2d. Inconsequent streams, or those which run independently 

 of existing slopes or dips, and which could not have been influenced 

 as to their positions in any very important manner by such slopes. 

 Again, these inconsequent streams may be subdivided into two 

 groups. 1st. Those which had their courses marked out prior to 

 the formation of the structural deformations through which they 

 run, regardless of the dip or slope of the strata. Such streams 

 may be called antecedent drainage, having been laid out before the 

 formation of the uplifts, and having successfully maintained their 

 prior right of way by cutting down their beds as fast as the obstacles 

 were elevated athwart their courses. 2d^ Inconsequent streams 

 may have been laid out upon the surface of strata which overlie 

 inconformably much more ancient beds. The upper strata being 

 m time denuded, the streams which at first were consequent, cut 



