Page:Popular Science Monthly Volume 12.djvu/425

Rh descends a funnel-shaped pipe eighteen feet in diameter at top, and seventy-eight feet deep. Both the basin and the tube are lined with silica, evidently deposited from the water. The natural inference is, that the mound is built up by deposit from the water, in somewhat the same manner as a volcanic cone is built up by its own ejections. In the intervals between the eruptions the basin is filled to the brim with perfectly transparent water, having a temperature of about 170° to 180°.

1. Immediately preceding the eruption sounds like cannonading are heard beneath, and bubbles rise and break on the surface of the water. 2. A bulging of the surface is then seen, and the water overflows the basin. 3. Immediately thereafter the whole of the water in the tube and basin is shot upward one hundred feet high, forming 3 fountain of dazzling splendor. 4. The eruption of water is immediately followed by the escape of steam with a roaring noise. These last two phenomena are repeated several times, so that the fountain continues to play for several minutes, until the water is sufficiently cooled, and then all is again quiet until another eruption. The eruptions occur tolerably regularly every ninety minutes, and last six or seven minutes. Throwing large stones into the tube has the effect of bringing on the eruption more quickly.

In magnificence of geyser displays, however, Iceland is far surpassed by the Yellowstone geysers in the basin of Firehole River. This wonderful geyser region is situated in the northwest corner of Wyoming, on an elevated volcanic plateau near the head-waters of the Madison River, a tributary of the Missouri, and of the Snake River, a tributary of the Columbia. The basin is only about three miles wide. About it are abundant evidences of prodigious volcanic activity in former times, and, although primary volcanic activity has ceased, secondary volcanic phenomena are developed on a stupendous scale and of every kind, viz.: hot springs, carbonated springs, fumaroles, mud-volcanoes, and geysers. In this vicinity there are more than 10,000 vents of all kinds. In some places, as on Gardiner's River, the hot springs are mostly lime-depositing; in others, as on Firehole River, they are geysers depositing silica.

In the upper geyser basin the valley is covered with a snowy