This immense body of water is kept up to this height for about 20 minutes, when it gradually recedes and again becomes quiescent. On the opposite side of the river is the Castle, so called from its resemblance to the ruins of a tower. It stands upon a platform measuring 75 by 100 ft. and 3 ft. in height, above which it rises about 12 ft. Prof. Hayden witnessed three eruptions of this geyser in 1872. The maximum height of the first was 34 ft., and of the second 93 ft.; that of the third was not ascertained. The eruptions lasted each about an hour and 20 minutes. The Giant geyser has a rugged crater, like a broken horn, 10 ft. in height and 24 by 25 ft. at the base. The top is about 8 ft. in diameter, with an irregular orifice of 5 or 6 ft. in width. The cone is open on one side, having a ragged aperture from the ground upward. Its discharges are irregular, and continue for irregular periods. When Prof. Hayden saw it in 1871, it played an hour and 20 minutes, throwing the water 140 ft.; but Lieut. Doane, who visited it the year before, states that it played 3 1/2 hours at one time, to a height varying from 90 to 200 ft. The Grotto, the Punch Bowl, the Riverside, the Soda, and the Fan geysers, and numerous others which have not yet even been named, merit notice.

There are wonderful groups also on the S. W. side of Shoshone lake, the head of one of the principal forks of the Shoshone or Snake river; and on Gardiner's river are some of the most remarkable springs in the world. The springs in action among the latter are not so numerous nor so powerful as those of the Fire-Hole basin, but are far more wonderful in their calcareous deposits, which exceed even those of the New Zealand geysers. In one place a hill 200 ft. high has been formed in a system of terraces, ornamented with semicircular basins, and with beadwork of beau-ful colors on a snow-white ground. These calcareous deposits cover an area of about two miles square. The active springs extend from the margin of the river to an elevation of 1,000 ft. above, the highest being 6,522 ft. above the sea. The geysers of the Fire-Hole basin are from 6,800 to 7,000 ft. above the sea. The valley of the Madison, with its branches, is shut in by high volcanic mountains, gashed with deep gorges, strewn upon their sides and at their bases with fragments of trachyte and obsidian, and covered with tall pines. Between the sources of the Madison and the Yellowstone these mountains rise to 9,000 or 10,000 ft. above the sea.

The valley of the Fire-Hole river is covered with the silicious deposits of the springs, and resembles an alkali flat. The bed of the stream is lined with white silica. Beneath this formation are lake or local drift deposits, and still lower basalt. The surface deposit is chiefly geyserite. The most of it is of an opaque white color, but in the lower basin pink specimens are found which are translucent. Some of it is greenish gray and some pearly, like enamel; and it assumes forms similar to those in Iceland. Some have a cauliflower-like form, and break very easily; others are beaded, and others covered with small stalagmitic processes. The texture varies from porous to compact, the most being porous and arranged in layers. The geyser cones are generally compact, and often have an enamellike coating. A specimen of the white geyserite, of cauliflower form, contained silica 83.83, water 11.02, chloride of magnesium 4; total, 98.85. The water contains very little solid matter. A specimen brought back by Dr. Peale was as clear as when bottled at the springs, showing no deposit; it contained 835 25/85 milligrammes of solid matter to the litre, consisting mainly of silica; chloride of lime and sulphate of magnesia were present in small quantity, and there was a slight trace of iron. -The geysers of Iceland are treated of in "Letters on Iceland," by .Von Troil (1772); " Travels in Iceland," by Sir George Mackenzie (1810);Journal of a Residence in Iceland during the years 1814 and 1815," by Ebenezer Henderson; Visit to Iceland in the Summer of 1834," by John Barrow, jr.; A Visit to Iceland," by the Hon. A. Dillon (1840); observations of M. Descloiseaux in Annates de chimie et de physique (April, 1847), and Philosophical Magazine" (vol. xxx.p. 397);Tracings of Iceland and the Faroe Islands," by R. Chambers (1856); A Yacht Voyage," by Lord Duf-ferin (London, 1858); Iceland, its Scenes and Sagas," by Sabine Baring-Gould (1863); The Land of Thor," by J. Ross Browne (1867); and "A Summer in Iceland," by C. W. Paijkull, translated from the Swedish by the Rev. M. R. Barnard (1868). For an account of the New Zealand geysers see Neu-Seeland, by Ferdinand von Hochstetter (Stuttgart, 1863). For geysers in the United States, see report of Lieut. G. C. Doane (1871), and the fifth and sixth annual reports of the"United States Geological Survey of the Territories," by F. V. Hay den (1872 and 1873).

The Giant Geyser.