224 IRVING. 



and most of all from the fact that the mountain has withstood 

 the degrading forces of erosion long after its lesser neighbors 

 have been worn away. 



The Needles. 



This porphyry uplift is situated some miles to the west of 

 Spearfish creek, between Bear gulch and Beaver creek. It con- 

 sists of a series of extremely sharp conical peaks, which have 

 a needle-like aspect, and which show the most perfect columnar 

 parting that the writer has seen in the Hills, with the excep- 

 tion of those exposed in the Devil's Tower. The columns are 

 vertical, and are broken across by a jointing, which shows a 

 rough resemblance to the ball and socket jointing of basalt. 



Three of these conical peaks are especially high, one of them 

 rising 500 feet above the bed of the creek below. 



Viewed from the south they bear, collectively, strong resem- 

 blance to a huge dike, but on ascending the highest of them, 

 one is impressed with the almost plug-like character of the mass. 

 The Carboniferous limestone can be seen to the east, north and 

 northwest, forming a wall about the uplift. On the west there 

 seems to be an extension of the porphyry. On the south 

 great blocks of indurated sandstone occur and the Cambrian is 

 extensively exposed in this direction. The Nigger hill Algon- 

 kian area is situated to the southwest, and it is probably to this 

 that the exposures of Cambrian are due. In between the lower 

 porphyry hills exposures of Cambrian shale occur, as if in its 

 intrusion the rock had included a portion of that series above 

 itself, and had elevated this to the level of the surrounding lime- 

 stone. The conical hills would then be the masses which had 

 filled the spaces below uplifted blocks of the massive, overlying 

 limestone. As maps were not available, no complete descrip- 

 tion of the uplift can be given, but from its general appearance 

 it seems to be in the nature of a vast upheaval with an extremely 

 irregular summit, due to the massive character of the rock be- 

 neath which it was intruded. 



