ANALYSIS OF ORES. 295 



Hematite iron ore exists in extensive deposits in the slates on Box 

 Elder, but is so intermixed with quartz as to greatly deteriorate its value. 



" Blue block" iron ore (siderite), weathering- to limonite, was found of 

 good quality in the black clay-shales of the Cretaceous on Beaver Creek. 

 The deposit covered quite a large area, and consisted of three horizontal 

 layers, respectively, 8 inches, 3 inches, and 5 inches thick, separated by a 

 few feet of clay-shales. This ore closely resembles the block ores of the 

 Coal Measures of Kentucky and Pennsylvania, which are worked in the 

 small charcoal iron-furnaces scattered through the timbered districts. 



Gypsum is found in beds from 5 to 12 feet in thickness, interstratified 

 with the red clays of the Red Beds. Usually there are three or four of 

 these layers of massive white or gray gypsum in the formation, but in places 

 they seem to be wanting and to be replaced by sandy clays. 



These Red Beds entirely surround the Black Hills, but are so exposed 

 by uplift on the southern and eastern sides as to conceal partially the gyp- 

 sum beneath the debris of the clays. 



In Redwater Valley, in the northwestern portion of the Hills, and in 

 the vicinity of Inyan-Kara and Sun Dance Hills, the gypsum beds are very 

 prominent, and the mineral occurs in extensive strata, so exposed as to be 

 easily mined should there ever be a demand for it. 



The Carboniferous limestone which covers a large area of the Black 

 Hills is very pure, and when burnt will make an excellent white lime suit- 

 able for building purposes. Building stone is everywhere abundant in the 

 Hills, and of good quality, including granite, slate, quartzite, sandstone of 

 all shades of color and degrees of hardness, limestone both white and gray, 

 and many varieties of trachyte and altered sedimentary rocks. 



Some of the soft variegated sandstone of the Red Beds is very orna- 

 mental, embracing every shade of color from yellow, through orange and 

 pink, to the darkest red. 



Springs, issuing from the black clay-shales of the Cretaceous on Beaver 

 Creek, were found to be strongly acid and astringent to the taste, turning 

 blue litmus red, and probably containing alum and free sulphuric acid. 

 Similar springs were reported to be found near Buffalo Gate, on the south- 

 eastern side of the Hills. A yellow efflorescence resembling flowers of sul- 



