GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 79 



260 feet above the level of the Yellowstone at the junction, and theyare 

 surrounded with pinnaclie-like columns, composed of the volcanic brec- 

 cia, rising- fifty feet above the falls and extending down to the foot, 

 standing like gloomy sentinels or like the gigantic pillars at the en- 

 trance of some grand temple. One could almost imagine that the idea 

 of the Gothic style of architecture had been caught from such carvings 

 of nature. Immense bowlders of basalt and granite here obstruct the 

 flow of the stream above and below the falls, and although, so far as we 

 can see, the gorge seems to be made lip of the volcanic cement, yet we 

 know that, in the loftier mountains, near the source of the stream, true 

 granitic as well as igneous rocks prevail. 



In the walls of the lower end of the Grand Canon, near the mouth of 

 Tower Creek, we can see the several rows of columns of basalt arrayed 

 in a vertical position, and as regular as if carried and placed in the sides 

 of the gorge l3y the hand of art. There is upon the surface a bed of vol- 

 canic breccia, then a row of vertical columns, then the cement with hot 

 spring deposits, then another row of columns. There are at least three 

 different series of the columns, while above and below to the edge of the 

 water are the volcanic and hot spring deposits. In the tongue that 

 runs down between the junction of the East Fork and the Yellowstone, 

 there is a singular hiitte cut off from the main range, Avhich at once at- 

 tracts the traveler's attention. The basis or lower portion of the hutte 

 is granite, while the summit is capped with the modern basalt, and 

 the debris on the sides and at the base is remarkable in quantity, and 

 has very much the appearance of an anthracite coal-heap. This huUe 

 will always form a conspicuous landmark, not only on account of its 

 position, but also from its peculiar shape and structure. Just below 

 the junction of the East Fork,abridge was constructed across the Yellow- 

 stone about a year ago, to accommodate the miners bound for the '' dig- 

 gings " on Clark^s Fork. It was evidently built with a considerable amount 

 of labor and boldness, for the river flows with great rapidity along the 

 narrow, rocky channel, and is about 200 feet in width. I make mention 

 of this bridge in this connection from the fact that it is the first and only 

 one as yet which has been erected across the Yellowstone Eiver, and 

 may in the future assume sonie historical importance. 



On the west side of the Yellowstone and west of Tower Falls, the 

 basalt is quite massive, sometimes forming columns quite irregular in 

 form and length, dii^'ering much from those on the opposite side. The 

 benches and irregular step-like terraces along the Yellowstone on both 

 sides, which are quite picturesque, are formed in part by the sliding 

 down of masses of earth from the margins of the canon. In the imme- 

 diate valley there is a recent drift deposit of sand and bowlders, often 

 stratified, made at a long period subsequent to the carving out of the 

 main channel through the volcanic rocks. The stratification and fine- 

 ness of the sediment would indicate still water, or moderately so, at 

 least. 



Soon after leaving Tower Creek, our road diverged to the westward of 

 the Yellowstone Eiver and crossed the northern side of the rim of the 

 basin proper, about a mile west of Mount Washburn, the highest peak in 

 this portion of the range. We followed a well-worn path up the north- 

 ern side, which led us up a slope so gentle that we were able to ride our 

 horses to the very summit. The ground is everywhere covered with 

 fragments of basalt and conglomerate, and at one locality there was an 

 abundance of fine specimens of chalcedony with malachite, (green car- 

 bonate of copper.) The volcanic rocks of this region contain some fine 

 specimens of mineral forms, of which silica is the base. There are grades 

 of exquisite beauty. Agates are common. 



