spijim; citioHK DisTificT. 239 



division of tlio Arclitran strata of the Black Hills. Wo liavo loft to tlio 

 south and west a rej^ion of fcldspathic, <»Tanite, mica schist, tal(tos(3 and 

 quartz schists, with crystalline or rose quartz, mica, g-arnets, and ii'l(lsi)ar 

 as the characteristic minerals, and enter a parallel belt of massive gray 

 quartzites, argillaceous and siliceous slates, in which tlu; [)rcvailiii^' minerals 

 of the schists are no longer seen. 



The change in the character of the rocks produces a corresponding 

 change in the topography of the region; the soft mica-schists had been 

 worn by erosion into broad parks and valleys, intervening with rounded 

 peaks and ridges of the harder strata, but the massive quartzites and hard 

 siliceous slates, resisting denudation, have been left in steep and high rocky 

 hills, through which the stream, winding and twisting among the peaks, has 

 cut a narrow gorge several hundred feet in depth. 



This ridge of hard slates and quartzites near the contact of the two 

 formations is an extension of the line of uplift of the Harney Peak range. 

 Although the granite does not extend as far north as this point by 

 several miles, yet the extreme hardness and uniformity in composition 

 of these rocks, enabling them to resist erosion, may be in part due to the 

 metamorphic action accompanying the intrusion of the granite forming this 

 range. Following the course of the stream, which soon enters a canon 

 among the higher peaks of the ridge, the dip of the formation is observed 

 to change from a general westerly direction to a well-marked easterly dip. 

 The sections of the quartzites exposed in the walls of the canon show a 

 contorted and irregular folding of the strata, but scarcely a quartz vein of 

 noticeable size occurs in the cliff's, although the composition of the rocks 

 is extremely siliceous ; a most decided contrast to the superabundance of 

 quartz distributed through the mica-schists of the older formation about the 

 heads of this stream. Spring Creek, emerging from the canon, winds 

 through a broad and beautiful valley, bordered by groves of pine for 

 nearly five miles. Long level tracts of fertile bottom lands, destitute of 

 trees and covered with a rank growth of the finest grass, extend on either 

 bank of the stream, while both on the north and south small open valleys 

 reach far back among the broken and rolling hills, the bright green grass 

 of these glades contrasting strongly with the darker color of the pine forest 



