holmes.] SNOW MASS GROUP. 65 



The rock of the peak proved to be an exceedingly fine and handsome 

 rhyolite, grayish in color, and containing many large crystals of white 

 feldspar. 



Station 23 was made near the highest point. This proved, as I had 

 expected, to be the extreme northern summit of the large group of 

 mountains that lies to the west of the Elk Mountains proper, and may 

 for convenience be called the West Elk group. It is hardly inferior to 

 the main range in area, and is separated from it by the valleys of Eock 

 Creek and East Eiver. Clusters of handsome, moderately high summits 

 could be seen far to the southward, and as far toward the east as Treas- 

 ury or Lookout Mountains. The general outlines and the manner of 

 weathering indicate that they are all of trachyte or rhyolite. 



To the westward the country is low, and slopes off toward the Gun- 

 nison Eiver on the left, and the Grand on the right. There are no 

 striking geographical features, and the whole visible area is doubtless 

 of Cretaceous age, the exposed rock being mostly of the Upper Creta- 

 ceous group, which comprises perhaps 2,500 feet in thickness of sand- 

 stones, conglomerates and shales, with an undetermined number of coal- 

 seams. 



As mentioned before, the main body of the stratified rocks about this 

 station are not disturbed, so that the exposures all along the eastern 

 base, beneath the body of trachyte, are horizontal, and so continue far 

 up Eock Creek. This creek heads in a picturesque group of moun- 

 tains far away to the east, cuts its way down through a number of deep 

 canons, and striking the base of this mountain turns abruptly to the 

 north. From this point we get our first view of the western faces of 

 the Elk Mountains, and are impressed more deeply than ever with 

 their beauty and grandeur. The lower slopes are underlaid by Creta- 

 taceous strata and densely covered by a growth of gray and purple 

 underbrush. Above this, groves of aspens and clusters of dark blue 

 pines relieve the glowing reds and purples of the Carboniferous rocks. 

 Still higher, and in delightful contrast to these ardent colors, are the 

 summits of gray granite, whose polished and ornate faces constantly 

 remind us of the form in some gothic cathedral. The culminating sum- 

 mits belong to the Snow Mass group, and are so thoroughly hemmed in 

 by serrated crests, and deep zigzagging ridges, that they seem to chal- 

 lenge approach. In a few days we hope to penetrate the obscure 

 valleys that headin this group, and from some of its higher peaks make 

 a more detailed study of its forms and structure. 



We found the ascent of Eock Creek beset with difficulties, and only suc- 

 ceeded in advancing at all by climbing the eastern wall of the canon and 

 remaining on a flat, shelf-like area, formed by the horizontal Cretaceous 

 strata. In the middle of the afternoon of September 1st, we descended 

 into the bed of a small tributary of Eock Creek, not far below the base 

 of Treasury Mountain. In passing down the face of the upper ledge 1 

 observed that the rock was of rhyolite, and not sandstone, as I had 

 supposed. This proved to be only a capping, and is doubtless a 'rem- 

 nant, separated from the mass west of the creek by erosion, since both 

 walls of the valley, up to corresponding horizons, are of Cretaceous 

 shales. 



The creek into which we had descended seemed to issue from the very 

 center of the Snow Mass group, and finding a pretty distinct game-trail 

 we turned to the left and followed it up the valley. On our left hand a 

 steep bluff rose to the height of some 1,500 feet. The strata exposed in 

 its face were probably of the Upper Cretaceous group, and consisted of 

 sandstones and shales, the former predominating above and the latter 

 5 H 



