GEYSERS. 



107 



Fig. 91.— Mackenzie's Theory of Eruption. 



91 represents a section through the basin, tube, and supposed cave. 

 Xow, if meteoric water should run into the cave through fissures more 

 rapidly than it can evaporate, it would accumulate until it rose above, 

 and therefore closed, the opening at a. The steam, now having no out- 

 let, would condense in the chamber b until its pressure raised the water 

 into the pipe, and caused it to overflow the basin. The pressure still 

 continuing, all the water 

 would be driven out of 

 the cave, and partly up 

 the pipe. Xow, the press- 

 ure which sustained the 

 whole column a d would 

 not only sustain, but 

 eject with violence, the 

 column c d. The steam 

 would escape, the ejected 

 water would cool, and 

 a period of quiescence 

 would follow. If there 

 were but one geyser in Iceland, this would be rightly considered a very 

 ingenious and probable hypothesis, for without doubt we may conceive 

 of a cave and conduit so constructed as to account for the phenomena. 

 But there are many eruptive springs in Iceland, and it is inconceivable 

 that all of them should have caves and conduits so peculiarly con- 

 structed. This theory is therefore entirely untenable. 



Bunsen's Investigations. — The investigations of Bunsen and his 

 theory of the eruption and the formation of geysers are among the 

 most beautiful illustrations of scientific induction which we have in 

 geology. Vie therefore give it, perhaps, more fully than its strict 

 geological importance warrants. 



Bunsen examined all the phenomena of hot springs in Iceland. 1. 

 He ascertained that geyser-water is meteoric water, containing the 

 soluble matters of the igneous rocks in the vicinity. He formed iden- 

 tical water by digesting Iceland rocks in hot rain-water. 2. He ascer- 

 tained that there are two kinds of hot springs in Iceland, viz., acid 

 springs and alkaline-carbonate spri?igs, and that only alkaline-car- 

 bonate springs contain any silica in solution. The reason is obvious ; 

 alkaline waters, especially if hot, are the natural solvents of silica. 3. 

 He ascertained that only the silicated springs form geysers. Here is 

 one important step taken — one condition of geyser-formation discov- 

 ered. Deposit of silica is necessary to the existence of geysers. The 

 tube of a geyser is not an accidental conduit, but is built up by its own 

 deposit. 4. Of silicated springs, only tliose with deep tubes erupt — 

 another condition. 5. Contrary to previous opinion, the silica in solu- 



