GEOLOGICAL SUEVEY OF THE TERRITOKIES. 129 



turies the hot springs also will gradually disappear ; for they too are 

 but a transient phenomenon in the eternal change of everything cre- 

 ated." — (Hochstetter's New Zealand, English translation, p. 432.) 



EXTRACT FROM BISCHOF'S " RESEARCHES INTO THE INTERNAL HEAT 



OF THE aLOBE.-' 



" No doubt can be entertained respecting the nature of the agent by 

 which the waters of the geyser, the Strokr, and other less considerable 

 springs, are thrown to such an immense height. It is, as in volcanoes, a 

 gaseous body, principally aqueous vapor. We may, therefore, very 

 fairly agree with Krug Von JSTidda, and consider volcanoes in the same 

 light as intermittent springs, with this difference only, that instead of 

 water, they throw out melted matters. 



" He takes it for granted that these hot springs derive their temper- 

 ature from aqueous vapors rising from below. When these vapors are 

 able to rise freely in a continual column, the water at the different 

 depths must have a constant temperature, equal to that at which water 

 would boil under the pressure existing at the respective depths ; hence 

 the constant ebullition of the permanent springs and their boiling heat. 

 If, on the other hand, the vapors be prevented by the complicated 

 windings of its channels from rising to the surface ; if, for example, they 

 be arrested in caverns, the temperature in the upper layers of water must 

 necessarily become reduced, because alarge quantity of it islost by evapo- 

 ration at the surface, which cannot be replaced from below. And any 

 circulation of the layers of water at different temperatures, by reason, 

 of their unequal specific gravities, seems to be very much interrupted 

 by the narrowness and sinuosity of the passage. The intermitting 

 springs of Iceland are probably caused by the existence of caverns, in . 

 which the vapor is retained by the pressure of the column of water in 

 the channel which leads to the surface. Here this vapor collects, and 

 presses the water in the cavern downward until its elastic force becomes 

 sufficiently great to effect a passage through the column of water which 

 confines it. . The violent escape of the vapor causes the thunder-like 

 subterranean sound and the trembling of the earth which precedes 

 each eruption. The vapors do not appear at the surface till they have 

 heated the water to their own temperature. When so much vapor has 

 escaped that the expansive force of that which remains has become less 

 than the pressure of the confining column of water, tranquillity is re- 

 stored, and this lasts until such a quantity of vapor is again collected 

 as to produce a fresh eruption. The spouting of the spring is therefore 

 repeated at intervals, depending upon the capacity of the cavern, the 

 height of the column of water, and the heat generated below." 



The various groups of mud-springs, or salses, which are described in 

 the preceding chapter are scarcely less interesting and instructive than 

 the geysers. The following analyses of the sediment, by Professor 

 Augustus Steitz, of Montana, for Mr. Langford, will be useful for com- 

 parison. The reader is also referred to the report of Dr. A. 0. Peale 

 in this volume. I have appended a few analyses of the hot-spring 

 deposits from New Zealand, from the interesting work of Dr. Hoch- 

 stetter. 



9 G s 



