236 58 



would not be possible if iiot water and steam, according to Mackenzie's theory, 

 rushed into the channel with great violence. This objection cannot now be main- 

 tained, as we know that the inlet to the geyser channel is situated 9- 10 m. from 

 the bottom. 



My explanation of the measurements of Bunsen and Descloizeaux also shows 

 that Bunsens theory that the temperature at a given spot in the channel continually 

 increases from one eruption to another, can no longer be held in its entirety. For 

 if we replace line II bj' the dotted line, then lines I to IV show that the tempera- 

 ture at a given point in the geyser channel does not rise appreciably from the 

 cessation of one eruption to the commencement of the next. 



The chief cause of the eruption is, therefore, to be sought outside the geyser 

 channel. Of course the energy accumulated in the channel will increase the power 

 of the eruption, but the calculations made by Bunsen to show that the water in 

 the channel is possessed of sufficient energy to sustain the eruption, do not, how- 

 ever, appear to me to be conclusive. 



It is very difficult to form even an approximate estimate of the amount of 

 energy required for an eruption, and besides this, the calculations do not provide 

 for the diminution of the available energy, produced by the intermixture of hotter 

 and colder water. 



Peale', who inclines perhaps most to Bunsen's theory, supposes, however, 

 that subterranean channels and cavities are of considerable significance in regard 

 to the geyser phenomena. 



Bunsen himself inclines to the opinion that in the case of Strokkur, — which, 

 as already pointed out, resembles "Stori Geysir" in many particulars, — the motive 

 power of the eruption is outside the channel. He has come to this conclusion 

 through the following observations. One can cause Strokkur to spout by stopping 

 up its channel with sods. This makes the jet of water at first discoloured, on 

 account of the dirt the water in the channel has received from the stoppage. But 

 after a short time the water becomes clear as a fresh supply of water flows into 

 the channel from other channels deeper down. 



In other respects Bunsen has been quite clear on the point that the typical 

 geyser channel is not the sole cause of the periodic eruptions. For instance, he 

 remarks in describing "Litli Geysir", that the eruptions of this spring are not due 

 to the same causes as those of "Stori Geysir". He seems to incline to the opinion 

 that the eruptions of "Litli Geysir" are most satisfactorily explained by Mackenzie's 

 theory. 



Mackenzie's theory is illustrated by Fig. 14. The cavity A is supplied with 

 water (of atmospheric origin) through fissures in the walls of the cavity. The water 

 in A receives heat partly conducted from the volcanic surroundings, and partly by 

 a supply of highly heated steam. At last the temperature in A becomes so high 



' Twelfth Annual Report of the U. S. Geological and Geographical Survey of the Territories. 

 Washington, 1883, p. 421. 



