GEOLOGICAL SUEVEY OF THE TERRITOEIES. 105 



covered with the snow-AvMte silica, which in the beauty and complete- 

 ness of the ornamentation surpasses the most intricate embroidery or 

 frost-work. About a mile south of the East Fork, on the head of 

 a little stream that flows into the Fire-Hole Eiver, is another of these 

 beautiful prismatic springs, which we called the Eainbow Springs. 

 A thin delicately ornamental rim of silica surrounds a basin 6 feet in 

 diameter, filled to the margin with perfectly clear water, and as the morn- 

 ing sunlight falls upon it, it reflects all the colors of the prism, 156o. 



Before leaving the group on the East Fork I will allude to a few more 

 that present some peculiarities. One spring keeps up an irregular spout- 

 ing. It commences quite strong and violent for about a minute, throw- 

 ing the water up about two feet, then it recedes into its crater with a 

 kind of cavernous gurgle, 193o. Another small geyser operates con- 

 stantly with a kind of subdued gurgle, 178^. Another gives forth a sup- 

 pressed, low, continuous gurgle, like that of a kettle of boiling mush, 

 193°. Not unfrequently there are three, and even five orifices in a single 

 basin, totally unconnected with each other. Sometimes one of them 

 will be perfectly quiescent while the others are in operation, and some- 

 times all are going at the same time. Sometimes a dead or dying spring 

 will be in close proximity to an active geyser, or a calm spriog, with a 

 temperature of 180° or 185°. Those springs that have a temperature 

 of 180° and upward, present the delicate bead or frost work of silica on the 

 inner sides of the basin, but when it is dim inished to 150°, or below, a 

 thick coating of iron is deposited. Many of the old springs have much 

 the appearance of huge tan-vats. In some of the basins the leathery 

 lining of the sides becomes torn into fragments, which wave to and fro at 

 every movement of the waters. These leathery masses, which are per- 

 fectly fragile in texture, like pulp in the water, become hard like pieces 

 of bark when dry, and are blown about by the wind. It is probably 

 composed of diatoms aggregated together, as the vegetable scum upon 

 a stagnant pool and covered, and perhaps the texture filled, with the 

 particles of oxide of iron. Between the East Fork and the Fire-Hole 

 Branch, a tongue or ridge extends down for a short distance from the 

 main range, composed mostly of a gray or yellowish-gray siliceous ma- 

 terial ; evidently an old hot-spring deposit. The trachy tic basalt also 

 crops out here and there, and, up in the higher portions of the mountains. 



Fig. 37. 



CRATER OF THUD GEYSER IN LOWER FIRE-HOLE IMMEDIATALY AFTER ERUPTION, LOWER GEYSER BASIN. 



prevails altogether. The broken hills that make up this ridge show, 

 however, that the history of these springs dates far back to the })eriod 

 of volcanic activity, for the si)riiig-doposits — conglomerates, volcanic 

 breccia, and trachyte — are all mingled together. High u]) in the hills, on 

 the south side of the ridge, are a few springs, which, in the early morn- 

 ing, send u}) large columns of steam. 

 We then passed over an area of a mile in width, covered with a 



