54 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



their origin. It is probable that the volcanic vent or point of effusion 

 was from the group of volcanic cones, in the high range, on the east 

 side of the Yellowstone, and that the dust, ashes, fragments of rocks, 

 &c., were thrown out into the waters of the lake, and deposited and 

 cemented into the apparently stratified condition they now present. The 

 style of weathering is much thp same as in ordinary conglomerates, and 

 at this locality several gorges, which have been worn by water deep into 

 the sides of the Jjutte, show the strata to incline 5° to 15°. By examin- 

 ing the valleys of the streams and ravines on either side of the mountain 

 ranges, we shall find upon what rocks, as a basis, this volcanic material 

 rests. On the north side of Trail Creek, we have the limestone ridges 

 full in view, the north side of the ridges sloping down into the plain 

 below the canon, while, on the south side, the edges of the limestone 

 strata project up nearly vertically, in sharp pinnacles worn out by 

 atmospheric forces. I think that these vertical limestones, for about four 

 miles in extent along this creek, afford an illustration of the breaking 

 down of the strata, like a table-leaf. Upon the plateau-like ridges 

 above are remnants of the more modern beds, as red clays, Jurassic, Cre- 

 taceous, and the Coal Series. The latter have been lifted up by a force 

 acting vertically. In the valley below are the outcropping edges of the 

 limestones, inclining at a small angle, but in such a way as to carry them 

 directly under the Basalt Butte. Indeed, the evidence is quite clear that, 

 underneath the ranges of volcanic mountains on the west side*of the Yel- 

 lowstone, exists a part at least and possibly all the unchanged rocks known 

 in this portion of the West. The effects of erosion are such all over this 

 country, that we cann ot assert the existence of the full series of sedimentary 

 strata unless they are visible to the eye. From the summit of Basalt 

 Butte the view is very beautiful and instructive. The valley of the Yel- 

 lowstone, from the lower caiion, far up above Bottler's Eanch, to the sec- 

 ond caiion, about thirty miles, has been the bed of one of the mountain 

 lakes. On the east side of the Yellowstone the eye takes in at a glance 

 one of the most symmetrical and remarkable ranges of mountains I have 

 ever seen in the West. Several of my party who had visited Europe re- 

 garded this range as in no way inferior in beauty to any in that farfamed 

 country. A series of cone-shaped peaks, looking like gigantic pyramids, 

 are grouped along the east side of the valley for thirty or forty miles, with 

 their bald, dark summits covered with perpetual snow, the vegetation 

 growing thinner and smaller as we ascend the almost vertical sides, until, 

 long before reaching the summits, it has entirely disappeared. On all 

 sides deep gorges have been gashed out by aqueous forces cutting through 

 the very core of the mountains, and forming those wonderful gulches 

 which only the hardy and daring miner has ventured to explore. This 

 range, which is called on the map Snowy Mountains, forms the great water- 

 shed between two portions of the Yellowstone Eiver, above and below 

 the first canon, and gives origin to some of the most important branches 

 of that river. Large numbers of springs and small streams flow down 

 from the mountains into the Yellowstone on the southwest side. Below 

 the first canon, but from the northeast side, flow the Big Bowlder, Eose- 

 bud, Clark's Fork, and Pryor's Fork, with their numerous branches. 

 This range continues on in a more or less broken condition to the south- 

 east, until it connects with the Big Horn Eange. From the summit of 

 Emigrant Peak, one of the highest of these volcanic cones, one great 

 mass of these basaltic peaks can be seen as far as the eye can reach, 

 rising to the height of 10,000 to 11,000 feet above the sea. Emigrant 

 Peak, the base of which is cut by the Yellowstone Eiver, is 10,629 feet 

 above tide-water, while the valley plain near Bottler's Eanch, on the op- 



