118 GEOLOGY. 



the year 1772, while Papandayang, one of the loftiest vol- 

 canoes in the island of Java, was in eruption, the mount- 

 ain, to the extent of 15 miles in length and 6 in width, 

 fell in with all its inhabitants, and wholly disappeared. 



202. Solfataras. There are localities in the neighbor- 

 hood of volcanoes, or where volcanoes formerly existed, 

 from which sulphur vapors arise, and result in incrusta- 

 tions of sulphur. Carbonic acid gas also often escapes 

 from the action of some acid, as the sulphuric, upon car- 

 bonate of lime or limestone. 



203. Geysers. Hot springs are very apt to occur in 

 volcanic neighborhoods, and when they are found where 

 there are no volcanoes, as in Virginia, there is evidence 

 in the character of the rocks that volcanic action has 

 been present at some time in the past. The famous hot 

 springs of Iceland are called geysers. In the Great Gey- 

 ser (Fig. 45) we have, in a mound of silicious rock, a ba- 

 sin-shaped cavity about fifty feet in diameter. From this 

 cavity there goes down perpendicularly into the earth a 

 pipe some eight or ten feet in diameter to the depth of 

 seventy-eight feet ; and in the eruptions of the geyser 

 there issues from this a huge column of water to the 

 height of 150, sometimes 200 feet. As the water mounts 

 up it is divided into numberless jets, and descends in 

 the form of spray, making an immense and splendid 

 fountain. The basin is sometimes empty, but is usually 

 filled with beautifully transparent water, boiling brisk- 

 ly. When the boiling is violent, and especially when 

 the issuing stream throws up the water, subterranean 

 noises are heard like the booming of distant cannon, and 

 the earth is slightly shaken. Each eruption is termina- 

 ted by a column of steam, which shoots upward with a 

 thundering noise. The hot water, from causes alluded 

 to in 116, dissolves some of the silica in the rocks 

 within, and as it falls deposits this, and thus forms the 

 mound. Much of the silicious matter is also deposited 

 in the region round about, the moisture being diffused 



