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 the shaft still open in the middle; and dry basins from which the water has receded with their shafts now choked with rubbish.

Geysers exist at the present time in many volcanic regions, as in the Malay Archipelago, Japan and South America; but the three localities where they attain their highest development are Iceland, New Zealand and the Yellowstone Park, U.S.A. The very name by which we call them indicates the historical priority of the Iceland group.

The Iceland geysers, mentioned by Saxo Grammaticus, are situated about 30 m. N.W. of Hecla, in a broad valley at the foot of a range of hills from 300 to 400 ft. in height. Within a circuit of about 2 m., upwards of one hundred hot springs may be counted, varying greatly both in character and dimensions. The Great Geyser in its calm periods appears as a circular pool about 60 ft. in diameter and 4 ft. in depth, occupying a basin on the summit of a mound of siliceous concretion; and in the centre of the basin is a shaft, about 10 ft. in diameter and 70 ft. in depth, lined with the same siliceous material. The clear sea-green water flows over the eastern rim of the basin in little runnels. On the surface it has a temperature of from 76° to 89° C., or from 168° to 188° F. Within the shaft there is of course a continual shifting both of the average temperature of the column and of the relative temperatures of the several strata. The results of the observations of Bunsen and A. L. O. Descloizeaux in 1847 were as follows (cf. Pogg. Ann., vol. 72 and Comptes rendus, vol. 19): About three hours after a great eruption on July 6, the temperature 6 metres from the bottom of the shaft was 121.6° C; at 9.50 metres, 121.1°; at 16.50 metres, 109° (?); and at 19.70 metres, 95° (?). About nine hours after a great eruption on July 6, at about 0.3 metres from the bottom, it was 123°; at 4.8 metres it was 122.7°; at 9.6 metres, 113°; at 14.4 metres, 85.8°; at 19.2 metres, 82.6°. On the 7th, there having been no eruption since the previous forenoon, the temperature at the bottom was 127.5°; at 5 metres from the bottom, 123°; at 9 metres, 120.4°; at 14.75 metres, 106.4°; and at 19 metres, 55°. About three hours after a small eruption, which took place at forty minutes past three o’clock in the afternoon of the 7th, the temperature at the bottom was 126.5°; at 6.85 metres up it was 121.8°; at 14.75 metres, 110°; and at 19 metres, 55°. Thus, continues Bunsen, it is evident that the temperature of the column diminishes from the bottom upwards; that, leaving out of view small irregularities, the temperature in all parts of the column is found to be steadily on the increase in proportion to the time that has elapsed since the previous eruption; that even a few minutes before the great eruption the temperature at no point of the water column reached the boiling point corresponding to the atmospheric pressure at that part; and finally, that the temperature about half-way up the shaft made the nearest approach to the appropriate boiling point, and that this approach was closer in proportion as an eruption was at hand. The Great Geyser has varied very much in the nature and frequency of its eruptions since it began to be observed. In 1809 and 1810, according to Sir W. J. Hooker and Sir George S. Mackenzie, its columns were 100 or 90 ft. high, and rose at intervals of 30 hours, while, according to Henderson, in 1815 the intervals were of 6 hours and the altitude from 80 to 150 ft.

About 100 paces from the Great Geyser is the Strokkr or churn, which was first described by Stanlay in 1789. The shaft in this case is about 44 ft. deep, and, instead of being cylindrical, is funnel-shaped, having a width of about 8 ft. at the mouth, but contracting to about 10 in. near the centre. By casting stones or turf into the shaft so as to stopper the narrow neck, eruptions can be accelerated, and they often exceed in magnitude those of the Great Geyser itself. During quiescence the column of water fills only the lower part of the shaft, its surface usually lying from 9 to 12 ft. below the level of the soil. Unlike that of the Great Geyser, it is always in ebullition, and its temperature is subject to comparatively slight differences. On the 8th of July 1847 Bunsen found the temperature at the bottom 112.9° C; at 3 metres from the bottom, 111.4°; and at 6 metres, 108°; the whole depth of water was on that occasion 10.15 metres. On the 6th, at 2.90 metres from the bottom it was 114.2°; and

at 6.20 metres, 109.3°. On the 10th, at 0.35 metres from the bottom, the reading gave 113.9°; at 4.65 metres, 113.7°; and at 8.85 metres, 99.9°.

The great geyser-district of New Zealand is situated in the south of the province of Auckland in or near the upper basin of the Waikato river, to the N.E. of Lake Taupo. The scene presented in various parts of the districts is far more striking and beautiful than anything of the same kind to be found in Iceland, but this is due not so much to the grandeur of the geysers proper as to the bewildering profusion of boiling springs, steam-jets and mud-volcanoes, and to the fantastic effects produced on the rocks by the siliceous deposits and by the action of the boiling water. In about 1880 the geysers were no longer active, and this condition prevailed until the Tarawera eruption of 1886, when seven gigantic geysers came into existence; water, steam, mud and stones were discharged to a height of 600 to 800 ft. for a period of about four hours, when quieter conditions set in. Waikite near Lake Rotorua throws the column to a height of 30 or 35 ft.

In the Yellowstone National Park, in the north-west corner of Wyoming, the various phenomena of the geysers can be observed on the most portentous scale. The geysers proper are about one hundred in number; the non-eruptive hot springs are much more numerous, there being more than 3000. The dimensions and activity of several of the geysers render those of Iceland and New Zealand almost insignificant in comparison. The principal groups are situated along the course of that tributary of the Upper Madison which bears the name of Fire Hole River. Many of the individual geysers have very distinctive characteristics in the form and colour of the mound, in the style of the eruption and in the shape of the column. The “Giantess” lifts the main column to a height of only 50 or 60 ft., but shoots a thin spire to no less than 250 ft. The “Castle” varies in height from 10 or 15 to 250 ft.; and on the occasions of greatest effort the noise is appalling, and shakes the ground like an earthquake. “Old Faithful” owes its name to the regularity of its action. Its eruptions, which raise the water to a height of 100 or 150 ft., last for about five minutes, and recur every hour or thereabouts. The “Beehive” sometimes attains a height of 219 it.; and the water, instead of falling back into the basin, is dissipated in spray and vapour. Very various accounts are given of the “Giant.” F. V. Hayden saw it playing for an hour and twenty minutes, and reaching a height of 140 ft., and Doane says it continued in action for three hours and a half, and had a maximum of 200 ft.; but at the earl of Dunraven’s visit the eruption lasted only a few minutes.

Theory of Geysers.—No satisfactory explanation of the phenomena of geysers was advanced till near the middle of the 19th century, when Bunsen elucidated their nature. Sir George Mackenzie, in his Travels in Iceland (2nd ed., 1812), submitted a theory which partially explained the phenomena met with. “Let us suppose a cavity C (fig. 1), communicating with the pipe PQ, filled with boiling water to the height AB, and that the steam above this line is confined so that it sustains the water to the height P. If we suppose a sudden addition of heat to be applied under the cavity C, a quantity of steam will be produced which, owing to the great pressure, will be evolved in starts, causing the noises like discharges of artillery and the shaking of the ground.” He admitted that this could be only a partial explanation of the facts of the case, and that he was unable