274 GEOLOGY OF THE BLACK HILLS. 



considerable stream, flowing, however, but a short distance before it sinks 

 and disappears. On lower Box Elder and on the divides along the valley 

 of Elk Creek there is considerable pine timber which has escaped the 

 extensive forest fires. The trees are, however, rarely above medium size, 

 growing very thickly together in dense groves. The rocks of this section 

 are clay-slates and quartzites, similar to those of the Spring Creek district. 



The occurrence of a broad belt of specular slates containing a large 

 percentage of hematite iron ore, which extends along Box Elder just above 

 the point where Custer's trail crosses it the second time, is peculiar to this 

 district. Over quite an extensive tract iron is present in the rocks in quan- 

 tities sufficient to strongly affect the compass. Thick strata of silicious 

 slates, on being followed, are gradually found to become more and 

 more ferruginous, until the rock is finally black and brilliant from 

 the excess of particles of specular iron. Frequently the hematite occurs 

 perfectly pure, interstratified in thin layers with white quartz, forming 

 a peculiar rock, the brilliant black of the bands of iron ore contrasting 

 strongly with the white stripes of quartz, resembling somewhat the 

 jaspery specular ore of Lake Superior, except that the interstratified 

 quartz is white and not red. These iron-bearing strata were upturned on 

 edge, and often 600 to 800 feet broad, with an unknown extent in the 

 direction of the strike. The hematite was so completely intermixed with 

 the quartz as to seriously injure the commercial value of the ore. The 

 thickest layers of pure specular iron which were seen did not exceed 

 three inches in width; and, except the presence of large quantities of silica, 

 the ore seems to be very pure and free from iron pyrites and phosphates. 



Near Custer Peak an immense ledge of massive milk-white quartz 

 extends north and south across the hills, conformable to the slates. Resist- 

 ing denudation, it caps the ridges for a long distance like a wall, and large 

 fragments detached from it cover the surface of the hill. Samples of the 

 quartz from this ledge were assayed by Mr. Ricketts, of the School of 

 Mines, but not a trace of gold was found in it. Where the slates are 

 extensively developed the quartz veins are generally thin and inconspicu- 

 ous. An occasional large ledge is, however, seen of the above character; 

 but among the belts of quartzites broad strata, transformed into impure 



