^g,j_^] GEOLOGY SNOW MASS MOUNTAIN. 261 



containing granitic pebbles, some of which are quite large. I have already 

 referred to the fact that Snow Mass Mountain and Capitol Peak are situ- 

 ated in an eruptive center that is distinct from the one in which White 

 Eock and Italia are included. The latter is more extensive and also more 

 irregular in shape. The amphitheater, on the eastern face of Snow Mass, 

 contains an extensive snow-lield, the largest I have ever seen on any peak 

 in the Eocky Mountains. It is from this snow-field that the mountain was 

 named. To the northeast of Snow Mass, on the east side of Snow Mass 

 Creek, is a high, bluff-like wall, which mustbe between 1,500 and 2,000 feet 

 high. The most remarkable feature in this wall is an immense bed of 

 eruptive rock, probably granite. At the base of the bluff, just above 

 the bed of the creek, are exposures of beds that from a distance I 

 judged to be Silurian. Fragments of these beds are also seen on the 

 opposite side of the creek resting dn the granite. The dike is about 

 600 or 800 feet in thickness, and has just below it what t think are Car- 

 boniferous beds, a,lthough on this point I cannot be certain, as they may 

 be Triassic. Al30ve the dike in some places is a capping of red sancl- 

 stone. This has been removed in other places by erosion. As we go 

 wsoutheast along the ridge the dike diminishes in thickness. The dike 

 I referred to as extending back of Maroon Mountain is probably an ex- 

 tension of this one. In the latter place, however, its dimensions are 

 much smaller. To prove that they are the same the line would have to 

 be followed. There are a great many of these dikes in the sedimentary 

 beds dipping away from the granite. The large one just referred to, 

 and shown in the illustration, is very easily explained. In the upheaval 

 of the granite the sedimentary beds were of course broken through, 

 and wherever there was no resistance the melted material intruded 

 itself. The planes of stratification afforded points of weak resistance, 

 and the beds were forced apart. Subsequent erosion, effected both by 

 water and by ice, has carried away so much material that the connec- 

 tion with the main mass has been cut across, and we have at present the 

 appearance as seen in the illustration. To fully investigate and work 

 up in detail all of these dikes would require that each one be followed 

 throughout its whole extent. Some of them would" probably be proved 

 to be trachytic, but I am of the opinion that if they could be traced to 

 the granite they would be seen to grade imperceptibly into it. I think 

 the entire mass of granite in the Elk Mountain district has been in 

 either a plastic or a melted condition, and that the granite is eruptive. 

 It is a question whether or not it is remelted metamorphic rock. The 

 future will have to decide tbis point. The elevation of the range was 

 Post-Cretaceous. The erosion since its elevation has been enormous. 

 The different peaks are connected by sharp, semicircular ridges, each 

 the ruin of a huge amphitheater, in the center of which the granite 

 appears. On some of these ridges the sedimentary beds form a capping. 

 The occurrence of these sharp ridges, high peaks, and these huge amphi- 

 theaters, renders traveling in the heart of the Elk Mountains extremely 

 rough. All the peaks are somewhat difficult of ascent. 



Looking northeast from Snow Mass Monntain, on the ridge beyond 

 the one in which the dike is seen, cappings of light-colored beds appear 

 along the summit. These are probably a portion of the Cretaceous beds 

 that slope from the Elk Mountains toward the valley of Eoariug Fork. 

 They will be referred to again in a subsequent portion of the chapter. 

 Ca})itol Peak is about three miles from Snow Mass, and has an elevation 

 of 13,<S16 feet. Judging from its appearance, as seen from Snow Mass, 

 it is similar in structure. West and southwest are the inverted beds 

 shown at / in Fig. 3, Plate XVIII. Northwest of the peak the rehUions 



