158 THE CHEMISTRY OF CREATION. 



consequence is, that the spring, by this con- 

 tinued process of deposition, increases in height, 

 until, reaching a certain altitude, it becomes 

 converted into a regular geyser. Surrounding 

 the tube formed in this simple manner, is a 

 hillock of silicious matter, formed by the over- 

 flowing of the water of the spring. These 

 tubes are fed with water from the mountains 

 above them, which becomes heated in the vol- 

 canic subterranean channels along which it is 

 conducted. This high temperature converts a 

 part of it into vapour, and the result is that the 

 water, elevated by its expansive force, foaming, 

 and hissing, rises up through the tube which 

 the incrusting waters have reared,' and rushes 

 boiling out of the mouth of the spring. Ice- 

 land abounds in these springs. 



But the Great Geyser, as is well known, is 

 an intermittent spring. Its phenomena are dif- 

 ferent from the smaller geysers or hot springs. 

 Instead of continually discharging a boiling 

 stream of water, as the other springs, an in- 

 terval of time occurs in its eruptions. The 

 cause of this has been generally explained to 

 be, the existence under ground of great caldrons, 

 in which steam accumulated, until its elastic 

 force drove up the water through the geyser 

 tube, after which it subsided again. But this 

 explanation is incorrect : the mouth of the Great 



