GEYSERS AND HOW THEY ARE EXPLAINED. 409 



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 fol- 

 lowed 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 min- 

 utes. 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 sur- 

 passed by the Yellowstone geysei-s 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 ba- 

 sin is only about three 

 miles wide. About it are 

 abundant evidences of pro- 

 digious volcanic activity 

 in former times, and, al- 

 though primary volcanic 

 activity has ceased, sec- 

 ondary volcanic phenom- 

 ena are developed on a 

 stupendous scale and of 



kind, viz. : hot 



Fig. 2. Chimney-like Vents (after Haydeu). 



every 



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 de- 



