South of the Thud Geyser is a large basin 150 feet in diameter, enclosing a crater twenty-five feet in diameter. From the inner crater the water is thrown up in a vast column sixty feet high, falling back in silver-white globules, a natural fountain of marvellous beauty. A short distance south of this Fountain Geyser is the most remarkable mud-pot in the Firehole valley. Its surface, forty by sixty feet in diameter, is covered with large puffs, which, in exploding with suppressed thuds, throw the hot mud several feet into the air and spatter the broad rounded rim in every direction. The mud is an impalpable silicious clay, of every shade of color from the purest white to a bright pink. Within a few feet of this mud-spring is a large clear spring sixty feet across, with perhaps fifty centres of ebullition. It is filled with the rusty, leathery deposit already described, and all around the basin where the waters overflow is an extensive deposit of iron.
A quarter of a mile east of the mud-springs, at the northwestern base of a mountain-spur and extending a thousand yards up a ravine, is a group of springs occupying a space five hundred yards wide. One of these, the Fissure Spring, is a hundred feet long and from four to ten feet wide. Quite a large stream flows from this spring. Many of the surrounding springs remain full to the rim, and are in constant ebullition, yet no water flows from them. Others discharge great quantities of water. In this group are three sulphur springs, the only ones in the region: the sulphur present however is not very abundant. Silica and iron seem to be the dominant constituents of nearly all the deposits. Some of the springs send forth a disagreeable odor, and deposit a curious black sediment like fine gunpowder. Near the centre of the group is a small lake 600 feet long and 150 wide. By its eastern shore is a geyser which spouts very regularly to the height of fifteen or twenty feet. West of the lake are two small geysers cones incrusted with a cauliflower-like formation; near them in a fissure are balls of geyserite coated in the same manner.
A thousand yards further south, in the southeastern corner of the basin, is a ravine a mile and a half long and three hundred yards wide, occupied by a most interesting group of springs and geysers. Just below the mouth of the ravine, on a mound fifteen feet high, is a large cone twenty-five feet high, probably a geyser. Steam issues steadily from the top with the sound of a high-pressure engine. It is called the White Dome Geyser.
In this lower basin there are very few raised craters, the most of the springs and geysers having funnel-shaped basins, with rims of various forms, but mostly circular. In this group there is besides the White Dome a small cone with its top broken off. It is four feet in diameter, with an aperture eighteen inches across. It is called the Bee-hive, For several feet around on all sides the surface of the ground is ornamented with pearly tubercles of silica, from the size of a pea to three inches in diameter. The spring basins in this group have every variety of form. One, a fine boiling spring, has an oval rim five feet by eight, its sides running straight down beyond the reach of vision. Another is funnel-shaped, tapering to a narrow aperture, with a scalloped rim, projecting several inches over the water. Some springs discharge no water; others send forth a stream two feet wide and six inches deep. In one of the streams, the channel of which is about two feet wide and one foot deep, the water is filled with a plant with a pinkish-yellow base, bordered with a very fine green silky fringe, perpetually vibrating with the flowing waters. "Except that they were a rich vegetable green, these fringes had the form and texture of the finest cashmere wool. The luxuriant growth of vegetation in and along the borders of these little streams," adds Dr. Hayden, "was a wonder of beauty. The whole view was there superior to anything of the kind I had seen."
In some of the springs Dr. Hayden's assistants found butterflies which had fallen in and been scalded to death. On taking them out they were found to be partially petrified, and coated with silica.
At the mouth of the ravine is the principal geyser of the group. Its basin is circular and about 60 feet in diameter, although the spring itself, which is in the centre, is only about 15 or 20 feet in diameter. The incrusted margin is full of sinuses, filled with hot water, which falls into them whenever the geyser is in operation. These pockets contain also smooth pebbles of geyserite, varying in size from that of a pea to a large-sized walnut, rounded by the action of the water. The water in the spring of the geyser is of a blue color and in constant agitation, though more violently so just before spouting. The column of water projected reaches the height of 100 feet, and is accompanied by immense clouds of steam.
Not far from this geyser is an elegantly scalloped spring, nearly circular, twenty-five feet in diameter, and with vertical sides to an unknown depth. The entire mass of the water is most violently agitated at times, and, overflowing the sides of the basin, passes off in terrace pools or reservoirs to the main stream, producing a system of architecture out of silica similar to that of the calcareous springs on Gardiner's River. The gay colors, from bright pink to delicate rose, are well shown.
The valley is filled with springs up to its very source; and springs which burst from the mountain side, eight hundred feet above the level of the basin, have temperatures ranging from 166° to 180°. Tracing one exceptionally cool stream up the south side of the cañon, Dr. Hayden found on the almost vertical side of the mountain a little spring so imbedded in bright green moss that it could hardly be seen.
"With great difficulty," he says, "we managed to climb up the mountain side, and, clearing away the moss, obtained the first water that we could drink for eight hours. In all of our examination during the day we had not found a drop of water of sufficiently low temperature to take into our mouths, though there were hundreds of the most beautiful springs all around us. We were like Coleridge's mariner in the great ocean, 'Water, water everywhere, but not a drop to drink.'"
Looking back over the valley the morning before his departure for the Upper Basin, Dr. Hayden saw it literally filled with columns of steam, ascending from more than a thousand vents. "I can compare the view," he writes, "to nothing but that of some manufacturing city like Pittsburgh, as seen from a high point, except that instead of the black coal smoke, there are here the white delicate clouds of steam. Small groups or solitary springs that are scattered everywhere in the woods, upon the mountain-sides, and which would otherwise escape observation, are detected by the columns of steam. It is evident that some of these groups of springs have changed their base of operations within a comparatively recent period; for about midway on the east side of the lower basin there is a large area covered with a thick, apparently modern, deposit of the silica, as white as snow, while standing quite thickly all around are dead pines, which appear to have been destroyed by the excessive overflow of water and the increased deposition. These dry trees have a most desolate look; many of them have fallen down and are incrusted with the silica, while portions that have fallen into the boiling springs have been reduced to pulp. This seems to be one of the conditions of silicification, for when these pulpy masses of wood are permitted to dry by the cessation of the springs, the most perfect specimens of petrified wood are the result. In one instance a green pine-tree had fallen so as to immerse its thick top in a large hot basin, and leaves, twigs, and cones had become completely incrusted with the white silica, and a portion had entered into the cellular structure, so that when removed from the water, and dried in the sun, very fair specimens were obtained. Members of my party obtained specimens of pine cones that were sufficiently silicified to be packed away among the collections."