RAWHIDE BUTTE. 27 



of o-ranitoid rocks, and its granite is similar in character to that of the 

 Laramie Range fifty miles southwest, and to that of the Harney Peak series 

 of the Black Hills, one hundred miles northeast. The ridge is about three 

 miles long, and has three principal peaks, the highest of whicli has an eleva- 

 tion above the sea of 6,300 feet, or about 1,200 feet above the base. It is, 

 however, but the southeastern termination of a long range of upheaval on 

 the headwaters of the Niobrara and Old Woman Fork mentioned in a sub- 

 sequent place. 



In detailed structure the Rawhide Butte consists of a series of black 

 micaceous schists or gneisses, with alternating strata of a coarse, very feld- 

 spathic granite. The lat- A^i 



ter range fi-om 2 to 20 or • Im^'^^^^^^^ t 



more feet in thickness, _ i^-^-"'^ i A V'^^^ /f^. 



and the whole dip 70° tosw. Sps. Mw\^ \ -^-^ ■^vW^I^Jr:^ ^^■ 

 75° toward the east, with ^ ^ 3 4545*54-5.. 5 1 



Fig. 1. — Section through R.Twhidc Butto. 

 a strike north 40 west. 1. Tertiary sands aud clays. 



mi •, • 1 2. Valley of Rawhide Creek. 



Ihe summit is covered 3. Graphic granite. 



.,, . /. 'I. Schists. 



With common pine Ot .'-,. l-Y-ldspathic granite. 



good size, and while the slope on the east side is gentle the descent on the 

 west is very abrupt. The structure is fairly illustrated by the annexed 

 illustration. 



On the extreme southeastern corner, occupying a position beneath all 

 the other strata of the butte, is exjiosed a bed of graphic granite (3), whose 

 junction with the overlying strata is curved irregularly. It is very similar 

 in character to the graphic granite met with in many places in the Harney 

 Peak region of the Black Hills. In it were found graphite, rose-quartz, and 

 tourmaline, and in the gneissic portions of the peak, black mica, red or pink 

 feldspar, and grains of magnetic iron. Seams or intercalated veins of quartz 

 are very numerous in the gneissic strata, running always with the stratifica- 

 tion of the rock. 



Around the western portion of the butte numerous fragments of the 

 Carboniferous limestone were found, but nowhere was it seen in place. 



The Tertiary strata which surround the ridge on all sides lie perfectly 

 horizontal, and in places are seen to lap high up on the ridge itself, while 



