emmons] PLATINUM IN COPPER ORES IN WYOMING. 95 
mine. A railroad is now building from Laramie City westward, which 
it is expected will eventually connect with Holmes. 
The mine is at present opened by a vertical shaft 200 feet deep, but 
at the time of visit, owing to certain changes which were taking place 
in machinery and ownership, the lower 100 feet were not accessible; 
hence a study of the unaltered ore must be postponed to a later date. 
A small matting furnace has been erected near the shaft for treating 
second-class ore. The ore shipped away from the mine is said to 
aggregate nearly 4,000 tons and to have assaj^ed 25 to -30 per cent cop- 
per. According to Professor Knight, it all contained more or less 
platinum. 
TOPOGRAPHY. 
The Medicine Bow Range is topographically a northwestern contin- 
uation of the Front Range of Colorado, which, as it enters Wyoming, 
spreads out into two forks that inclose the broad valley known as the 
Laramie Plains. The eastern boundary of these plains is formed by 
the Black Hills of Wyoming, sometimes known as the "Laramie" 
Hills — a north-south uplift of older rocks, mainly granite, which ends 
at the north bend of the North Platte River, where these rocks dis- 
appear under Mesozoic sediments. 
The Medicine Bow Range on the west likewise dips down under the 
Mesozoic sediments and is lost as a range, its almost isolated northern 
point being known as "Elk" Mountain. As seen from the Laramie 
Plains a striking feature is the plateau-like structure of the main mass 
of the uplift. On its eastern flanks it rises abruptly from the plains 
about 2,000 feet; then slopes back almost at a level with an average 
elevation of 9,000 to 10,000 feet to the central uplift around Medicine 
Peak, which is again about 2,000 feet above the plateau. 
This plateau-like portion of the range is, for the most part, covered 
with a comparatively abundant forest growth, and its streams run in 
shallow swale-like valleys which change rapidly to deep rocky gorges 
in their lower courses as they leave the plateau. At Holmes, which 
is on the higher part of the plateau, the forest covering is unusually 
dense and the rock surface is covered by to 16 feet of wash, so that 
rock outcrops are rare and iirospecting has to be done by trenching 
and shaft sinking, and the geological relations are correspondingly 
difficult to decipher. 
GEOLOGY. 
In its geological composition and structure the Medicine Bow Range 
appears to resemble more closely the Encampment Mountains on the 
opposite side of the Platte Valley than the Colorado ranges, and there 
is some reason for assuming that the two once formed part of one and 
the same mountain uplift, and that their separation by the cutting of 
the Platte Valley has been of comparatively recent geological date. 
The principal distinction from the other ranges that have a core 
