PARK RANGE, 135 



characteristic of the Medicine Bow series, which was referred to the Huro- 

 nian formation. 



A characteristic granite from the southern end of the range is found 

 upon the summit of Ethel Peak. It is a moderately coarse-grained rock of 

 a reddish-gray color, and a somewhat friable texture, breaking up readily 

 into small, irregular-shaped pieces. It is distinctly bedded, but without any 

 lamination in the arrangement of its constituents, and closely resembles 

 many of the granite bodies from the Colorado Range. It is composed of 

 quartz, feldspar, and mica. The quartz is present in small angular grains, 

 slightly tinged with gray ; the feldspars, mostly orthoclase, are reddish in 

 color, and frequently stained with an earthy, ferruginous coating, while the 

 mica, in dark biotite plates, is not very abundant, but well disseminated 

 through the mass, occasionally adhering to the broad faces of the orthoclase 

 crystals. The outlying spur east of Arapahoe Creek, where observed, is a 

 somewhat similar-appearing granite, a reddish, crumbling mass, with rounded 

 outlines, which probably belongs to the same body. Separated from this 

 spur by the broad valley of Arapahoe Creek, stands Crawley Butte, an 

 isolated and prominent landmark in the North Park. It rises above the 

 Tertiary plain some 1,000 or 1,200 feet. Geologically, it is closely con- 

 jiected with the spur, and the eroded forms and outlines are similar in both 

 masses, being the result of the same agencies upon rock-masses of the same 

 composition and texture. 



On the northern rim of the Park, granites would seem to be the 

 prevailing rock. From Bruin Peak, the highest summit of this ridge, 

 were collected a number of interesting rocks. Coarse-grained graphic 

 granite occurs, similar to that found in Grand Encampment Canon, and on 

 the west side of Long's Peak, in which the individual crystals of quartz, 

 feldspar, and mica have frequently attained the dimensions of half an inch 

 or more in diameter. The feldspar is chiefly orthoclase, of a bright red 

 color, and the quartz massive and usually white. Both muscovite and black 

 biotite are present, the plates of the former being much the larger. One 

 variety of this rock is made up mainly of flesh-colored orthoclase, with but 

 little quartz or mica, and these are usually present in segregated masses. 

 Between the feldspar masses occui- narrow fissures of yellowish-green epidote. 



