BLACK HILLS GEOLOGY. 193 



gulch of Annie creek which flows into Spearfish almost directly 

 from the east. As we follow the stream up its course two 

 branches enter it. Ross Spring creek, its most northerly tribu- 

 tary, which heads up in the elevated region around Crown hill, 

 has cut a deep ravine through the limestone into the underlying 

 sediments of the Cambro-Silurian. Lost Camp creek, the most 

 southerly with its numerous branches, rises in the broad am- 

 phitheatre on the western slopes of Terry Peak. Between 

 these two streams are the waters of Annie creek itself, which 

 heads up almost to the town of Portland, and is separated 

 from the headwaters of Squaw creek by quite a narrow divide. 

 Between this stream and Lost Camp creek rises the prominent 

 rounded crest of Foley Mountain, which is connected with 

 Terry Peak by a high semicircular divide, capped by a series 

 of low dome-like knolls and enclosing a portion of the pre- 

 viously-mentioned amphitheatre. 



To the south of Lost Camp creek, and separated from it by 

 a low limestone ridge, are the two short, but precipitous gorges, 

 which are occupied by Sweet Betsy creek, while still further to 

 the south, and heading up into Terry Peak to the west of the 

 Foley Flat amphitheatre, is the wild, deep ravine of Raspberry 

 gulch. 



If now we turn to the eastern slopes of the Terry Peak water- 

 shed, we are most forcibly impressed by the striking contrast 

 between the two topographies. Instead of the narrow precip- 

 itous gorges with high, flat, table-like divides intervening, there 

 is a great assemblage of irregular hills and divides of all shapes 

 and sizes, and of so irregular a character as to completely baffle 

 collective description. Nor is this contrast in any way confined 

 to this district, but it will be noticed in every case where we 

 pass from the Carboniferous plateau to the districts of Cambrian 

 shale, with their vast confusion of dikes, sheets, and irregular 

 intrusive bodies, a fact which emphasizes the inseparable con- 

 nection between geological structure and the degrading forces 

 of erosion. 



On the southeastern slopes of Terry Peak and Deer Mountain 

 the head waters of White -tail creek have their origin, and flow 



