MEDICINE BOW RANGE. 97 



pure white quartzite, are very striking. The valley of French Creek, on 

 the south side, may be especially mentioned; here the escarpment is 1 ,500 feet 

 in height, and the basin-shaped caiion, with its glacially-eroded lake-bottom, 

 presents a fine example of ice action upon brittle, massive quartzite, which 

 splits and breaks up easily into blocks under the action of frost and ice. 

 There are ridges here entirely covered with huge blocks of quartzite, many 

 tons in weight, piled up in the most irregular manner, and one may travel 

 long distances without finding any rock in place. 



Coniferous forests cover the greater part of the Medicine Bow Range, 

 and there are many large areas, especially in the regions north and east of 

 Medicine Peak and the headwaters of the Little Laramie River, where 

 tree-growth is quite dense. Already much valuable timber has been cut. 

 AMes Bouglasii, a tall graceful tree, often over 100 feet in height; Abies 

 Engelmanni, known as "white pine", and Pinus ponderosa, or "yellow pine", 

 are among the species found. The timber-line, as in the Colorado Range, 

 may be placed at 11,000 feet above sea-level. 



Geology. — Like the Colorado Range, the Medicine Bow is made up 

 almost exclusively of Archaean, highly crystalline rocks; but while in their 

 genieral habit they resemble the formations of the eastern range, they 

 exhibit certain mineralogical and petrographical differences, that are char- 

 acteristic of the entire range. All the varieties of rocks observed may be 

 classed under the following heads: granites, gneisses, hornblende-schists, 

 mica-schists, dioritic schists, slates, argillites, quartzites, chert, hornstone 

 conglomerates, and limestone. All the larger bodies of true granite appear 

 to be confined to the southern end of the range, where it is closely con- 

 nected with the Colorado Range and the borders of the North Park. Even 

 these, however, show more or less tendency to bedding with the constit- 

 uent minerals arranged in parallel bands and layers, and passing into a 

 gneissic structure. A typical granite of the North Park ridge occurs on 

 the summit northwest from Clark's Peak. It is a fine-grained compact 

 rock, with a uniform texture, and a sharp angular fracture. In color, 

 it is dark gray. It is composed of translucent quartz, white and pearl- 

 colored feldspars, and dark thin plates of mica. Both orthoclase and 

 plagioclase are present, the latter very abundant; deep red orthoclase, so 

 7 D a 



