272 GEOLOGY OF THE BLACK HILLS. 



there were no more elevated gravel bars seen, but along the banks of the 

 creek gravel flats extend as far at least as the outermost ridge of foot- 

 hills. 



I consider that the Rapid Creek district, including Castle Creek, is 

 destined to be one of the most productive in the Black Hills. For forty 

 miles along its course its banks are bordered by deep and extensive 

 placers, forming the largest gravel deposits on any stream in the Hills. 



SECTION V. 



BOX ELDEB AND ELK CBEEKS. 



Proceeding north from Rapid Creek, a quite extensive area is passed 

 over, which, while geologically a continuation of the clay-slate and quartzite 

 belt, presents in its more level surface a strong contrast to the rocky and 

 broken region to the south. This section is drained by two small streams, 

 Box Elder and Elk Creeks, whose largest branches head almost at the very 

 base of Custer Peak. 



A view from the top of Custer shows a comparatively flat country, with 

 low, rolling hills; in places groups of small broken peaks are noticed; but 

 the topography is very different from that of the region about the forks of 

 Rapid and Spring Creeks, where sharp serrated peaks rise, one beyond 

 another, as far as the eye can reach, only exceeded in height and magni- 

 tude by Harney itself. It is a desolate-looking country. Most of the 

 timber has been destroyed by fire and large areas are covered with dead 

 pines. To the east, at a distance of ten or twelve miles, the limestone is 

 seen crossing the hills in an irregular line in a northwesterly direction, and 

 many of the slate ridges and peaks are, near the outcrop of the limestone, 

 capped by it and the Potsdam sandstone — the remnants of the great sheet 

 of Paleozoic rocks which once covered this area and has since been 

 removed by erosion. 



From the base of Custer Peak the course of each creek can be traced 

 until it canons in the limestone, generally flowing through small open 

 valleys or broad grassy swales, which in places, however, are contracted 

 into a rocky gorge in cutting across the occasional strata of hard quartzites. 



