148 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



crest are almost entirely destitute of timber of any kind, but are covered 

 over with sliort grass. The ascent from either side is so gradual that 

 it is difficult to detect the fact that one is passing over the water-shed 

 of the continent. Eocks of all ages, from the Carboniferous to the most 

 modern, Tertiary inclusive, are found. 



After passing the divide, we descended the Medicine Lodge Creek 

 toward Snake Kiver Basin. In the Carboniferous limestones on both 

 sides of the valley, the fossils were quite abundant. Among them was 

 a variety of corals, and several species of Frodiictus^ among them P. 

 semireticidatus, &c. The surface, as far as the eye can reach on either 

 side, is extremely rugged, raised into ridges, and cut into deep canons. 

 Here and there a fine dome-shaped peak rises high above all the rest, 

 9,000 to 10,000 feet above the level of the sea. The Medicine Lodge 

 Creek commences in little bogs or springs near the divide, and soon the 

 aggregated waters from numbers of little side-valleys, extending down 

 from among the hills and ridges on both sides, form a good-sized trout- 

 stream. I think I never saw a stream, large or small, more fully crowded 

 with trout. There were two species, each equally abundant ; and yet this 

 stream sinks beneath the surface and is lost entirely twenty-five miles 

 before reaching Snake Eiver. The limestones and quartzites seem to 

 monopolize the country" for a belt of thirty to fifty miles in width, 

 extending east and west on both sides of the divide. 



Our camp was made in a singular basin, a sort of synclinal depression, 

 an average of three miles in width and about eighteen miles long, cov- 

 ered over with grass, but no timber, scarcely a shrub. The valley must 

 be at times a complete marsh or bog. It is covered Avith singular sink- 

 holes. They are round holes ten feet below the surface, and full of 

 rounded bowlders; and in the spring of the year, when the snows 

 on the sun^ounding hills melt, there is a great accumulation of water, 

 which in the autumn passes away to the main water-courses, among the 

 bowlders underneath the superficial deposit of soil. We see, therefore, 

 that on the very summit of the Ilocky Mountain divide, the Pliocene 

 lake deposits occur, as well as immense accumulations of the local drift 

 or Quaternary. 



At some future period, in a general resume of^ the geology of the West, 

 these statements will be referred to. In my preliminary reports I desire 

 to confine myself mostly to a simple statement of what I saw along the 

 route, that the observations may be placed on record lor future use. 

 Our first camp on Medicine Lodge Creek was G,110 feet above the sea. 

 The high mountain hills on either side are 800 to 1,500 feet above the 

 valley, some of the highest peaks 2,500 feet or more. One high ridge of 

 Carboniferous limestone was found to be 700 feet above camp, by barom- 

 eter. One of the principal features of this valley is a most remarkable 

 deposit from springs, which must liave occurred far back in the Pliocene 

 period. It is far the largest I have ever seen in the West, and may serve 

 to illustrate the influence which springs may have in the formation of the 

 earth's crust. It seems to have filled up a synclinal trough. The Car- 

 boniterous limestones incline from the sides of the mountains that inclose 

 the valley, and the deposit is arranged in nearly horizontal layers, jut- 

 ting up against the sides of the valley, while the stream itself has cut its 

 channel through it, thus exposing a fair section to the eye. On the east 

 side of the creek, the wall is 100 to 200 feet high, made up of rather 

 massive layers of most beautiful white limestone, some of it porous like 

 heavy tufa, but most compact like the old Hot Spring limestone on Gar- 

 diner's Eiver. Above it, and conforming to the bed of limestone, are 

 about 80 feet of gray volcanic ash, forming a soft, sometimes jDorous, 



