46 GEOLOGICAL SURVEY OF THE TERRITORIES. 



be 1,500 feet of Silurian strata, and 2,000 feet of Carboniferous beds. 

 The upper portion of the latter is nearly all coarse, rusty, or gray sand- 

 stone, while the lower half contains many beds of shale, with layers of 

 limestone containing great numbers of well-marked Carboniferous fossils, 

 as TriloMtes and Froductus. 



In the Silurian group the first bed of trachyte is quite massive, and 

 must correspond with that seen on the west side of the range. The 

 jointage is perfect, and the mass breaks into huge cubical blocks. Some 

 of it is laminated vertically, as if composed of thin layers tipped on end. 

 Higher up are several beds of the trachyte, varying from 15 to 30 feet 

 in thickness. It was not possible to fix a line between the Silurian and 

 the Carboniferous groups, in most instances. I shall only speak of these 

 formations in general terms, referring the reader to the carefully- wrought 

 section in Dr. Peale's report. As a general rule, it is only at the very 

 heads of these gulches that the basis rock can be seen. The process of 

 grinding to powder, as it were, by ice and water, has been carried on to 

 such an extent that the entire valley is covered thickly with earth, filled 

 with more or less worn rocks, of every size, from that of a pea to several 

 feet in diameter. The snow, melting upon the crests of the mountains, 

 saturates these superficial earths with water, and they slowly move down 

 the gulch much like a glacier. This is another process of grinding 

 the underlying rocks, smoothing and grooving them. Underneath these 

 suj)erficial deposits is what the miners call the " bed-rock," and it often 

 involves immense labor to strip them off to reveal the mineral lodes. 



As we pass down Horseshoe or Four-mile Creek we soon find that 

 the vast amount of loose material covers everything, rendering the suc- 

 cession of strata very obscure above theCarboniferous, yetwe know that 

 there is a full series of the red beds, Jurassic and Cretaceous, up to the 

 summit of the Lignitic group, inclusive. The upper group inclines away 

 from the base of the main Park range far eastward into the Park. Pass- 

 ing northward from Fairplay to the Little Platte or Twelve-mile Creek, 

 we find the foot-hills correspond to the more modern sedimentary beds, 

 incliniug at all angles. In the channel of a little stream, about ten miles 

 south of Fairplay, the Triassic and Jurassic beds are exposed to some 

 extent, dipping 30° to 40° east or southeast. The foot-hills all along the 

 west side of the Park appear to be comx^osed mostly of the red group, 

 lapping on to the sides of the mountain. The Carboniferous and Silu- 

 rian groups are seen on the sides and summits, higher up. A few of 

 these details will aiford us a glimpse of the wonderful complication of 

 forces that have thrown these mountains into chaos, as well as the tre- 

 mendous power of the eroding agents which have aided to increase the 

 difficulties in some localities and to decrease them in others. As we 

 move westward to the Sawatch range, or the Elk Mountains, we shall 

 meet with a repetition of the same results, only on a far grander scale. 



South of Horseshoe Mountain the main range continues 12,000 feet 

 and upward to Buffalo Peak, rising far above timber-line. The rocks 

 are mostly granitoid, but there are remnants of the quartzites even on 

 the crest ; but rather low down on the sides, perhaps 1,000 feet below 

 the crest, the Silurian limestones and quartzites crop out here and there, 

 though much obscured by the debris. In the valley of the Little Platte, 

 close to the foot of the mountains, is a considerable thickness of a group 

 of very peculiar gypsiferous strata, the same as those arotind the salt- 

 works about twelve miles to the southeast. The surface has a volcanic 

 appearance, as if covered with slag, and yet the clays, sands, and other 

 rocks of both the Cretaceous and Jurassic are incrusted with the 

 chloride of sodium as well as the sulphate of lime. Again, on the 



