GEOLOGICAL SUKVEY OF THE TEKRITOKIES. 87 



basins, with, a thick deposit of iron on tlie siiles, lining the channel of 

 the water that flows from them. These vary in temperature from 98° 

 to 120°. The highest temperature was 192°. The steam-vents are very- 

 numerous, and the chimneys are lined with sulphur. Where the crust 

 can be removed, we find the under side lined with the most delicate crys- 

 tals of sulphur, which disappear like frost-work at the touch. Still there 

 is a considerable amount of solid amorplioiis sulpliur. The sulphur and 

 the iron, with the vegetable matter, which is always very abundant 

 about the springs, give, through the almost infinite variety of shades, a 

 most pleasing and striking picture. One of the mud springs, with a basin 

 20 by 25 feet and 6 feet deep, is covered with large bubbles or puffs con- 

 stantly bursting with a thud. There are a number of high hills in this 

 vicinity entirely composed of the hot-spring deposits, at least nine-tenths 

 silica, appearing snowy-white in the distance; one of the walls is 175 feet 

 high, and another about 70 feet. They are now covered to a greater or less 

 extent with pines. Steam is constantly issuing from vents around the base 

 and from the sides of these hills. There is one lake 100 by 300 yards, with 

 a number of bubbling and boding springs arising to the surface. Near 

 the shore is one of the sieve-springs, with a great number of small per- 

 forations, from which the water bubbles up with a simmering noise ; 

 temperature, 188°. This group really forms one of the great ruins. 



We will now return to the falls, and pursue our way up the valley of 

 the Yellowstone to the lake. We wound our way among the dense 

 pines that clothe the foot-hills, and, striking a game-trail, succeeded in 

 avoiding the marshy bottoms of the river. Great nujubers of small 

 springs seem to flow out of the sides of the hills, and distribute them- 

 selves over the bottom, finally draining into the river. The deep snows 

 which fall on the mountains, and continue the greater portion of the 

 year, melt so gradually that these springs have a constant supply, aiid 

 during the summer the grass and flowers give to the lowlands a meadow- 

 like appearance by the freshness and vividness of the colors. The river, 

 by its width, its beautiful curves, and easy flow, moves on down toward 

 its wonderful precipices with a majestic motion that would charm the eye 

 of an artist. Some of the little streams which we crossed on our way 

 up the river were full of fresh-water shells. Wherever the water stands 

 for a time, the surface is covered with a yellow scum from the presence of 

 iron. About five miles above the fails, on the east side of the river, we 

 crossed a small stream which held a large amount of alum in solution, 

 and on this account was appropriately named Alum Creek. This little 

 stream is 2 feet wide and 2 inches deep, as clear as crystal, and, as it flows 

 along through the rich grass, it would not be noticed by the traveler that 

 it differed from any other stream, except by the taste. Ever since descend 

 ing into the basin we have met with great quantities of a kind of obsidian. 

 It seldom occurs in a compact, amorphous, crystalline mass, like opaque 

 glass, but as an aggregate of small amorphous masses, easily disinte- . 

 grating, so that the surface is covered with the small obsidian pebbles. 

 The color is black or dull purplish-black. There are exposures here and 

 there of the basalt also; some of it contains great quantities of rounded 

 masses, like concretions, from the size of a pea to 10 inches in diameter; 

 they seem to be little geodes, found in the igneous mass, lined inside 

 with crystals of quartz. These masses are sometimes called "volcanic 

 walnuts " by travelers. 



About ten miles above the falls, on the east side of the Yellow- 

 stone, we came to a most interesting group of hot springs, named, 

 in Lieutenant Doaue's report, the " Seven Hills." The chart which 

 accompanies this report will show the location of the hills and the 



