GEYSERS AND HOW THEY ARE EXPLAINED. 413 



evaporate, it would accumulate until it rose above, and therefore 

 closed, the opening at a, The steam, now having no outlet, 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 continu- 

 ing, all the water would be driven out of the cave, and partly up the 

 pipe. Now, the pressure 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 with- 

 out 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 incon- 

 ceivable that all of them 

 should have caves and 

 conduits so peculiarly 

 constructed. This the- 

 ory is therefore entirely 

 untenable. 



The investigations 

 of Bunsen and his theory 

 of the eruption and the 

 formation of geysers are 

 among the most beauti- 

 ful illustrations of sci- 

 entific induction which we have in geology. We 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 as- 

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

 springs and alkaline-carbonate springs, and that only alkaline-carbon- 

 ate 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 dis- 

 covered. 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 those with long tubes 

 erupt another condition. 5. Contrary to previous opinion, the silica 

 in solution does not deposit on cooling, but only by drying. This 

 would make the building-up of a geyser-tube an inconceivably slow 

 process, and the time proportionally long. This, however, is not true, 

 for the Yellowstone geyser-waters, which deposit abundantly by cool- 

 ing, evidently because they contain much more silica than those of 



Fig. 7. Mackenzie's Theory or Eruption. 



