254 Dr Charles Daubeny on the 



the surface. Neither can the almost constant escape of azotic gas be 

 accounted for, without supposing some process of oxygenation to be 

 going on in the interior. 



Now these springs usually make their appearance, where other 

 evidences of volcanic action are exhibited, in the dislocation and eleva- 

 tion of the surrounding strata ; and the latter phenomena occur so 

 extensively over the earth's surface, that volcanic operations, if as- 

 sumed to be their cause, may have been widely enough distributed to 

 produce a general increase of temperature throughout that zone in 

 the interior of ,the globe in which they are carried on. What may 

 be the condition of the earth lower than this, we surely have no data 

 for ascertaining ; for it is evident that, if this supposed zone lie be- 

 low the level which mining operations have reached, it would itself 

 elevate the temperature of all those portions of the earth's crust of 

 which we have any cognizance. 



I am, however, unwilling to dogmatize, either with respect to the 

 general cause of the internal heat of the globe, or the limits to which 

 this heat may be confined. 



All that I have ever sought to prove is, that, be the existence of 

 a central heat ever so well established, its assumption does not ad- 

 vance us towards the explanation of the phenomena, either of volca- 

 noes, or of thermal springs in general, and that a process of oxidation 

 is going on, often with intense energy, in the interior of the globe, 

 of a different nature from that usually occurring on the surface, as 

 being attended with an evolution of hydrogen gas, a phenomenon 

 which can be most readily explained by the decomposition of water, 

 through the action of the metals of the earths and alkalies upon that 

 liquid. 



I would finally remark, that Professor Bischof will find his objec- 

 tion to the supposed existence of these bases in the interior of the 

 globe, arising from their low specific gravity, answered by anticipa- 

 tion in my Reply to his former paper, as I have there shewn that the 

 specific gravity of one hundred parts of the metallic principles pre- 

 sent in a mass of ordinary lava, would be quite as considerable as 

 that of the same amount of these same bodies united with oxygen, 

 so that the diflSculty, be it small or great, which attends the fact of 

 the high specific gravity of the globe, as compared with that of the 

 materials composing its surface, is the same to those who reject my 

 hypothesis, as to those who embrace it. 



Lest, however, it should be imagined that I have attached an un- 

 due weight to this theory, or have done more than to advocate it as the 

 most plausible account that can at present be given of the facts before 

 us, I will, in conclusion, extract the remarks which I made, nearly 

 ten years ago, in my Report on Mineral and Thermal Springs, un- 

 dertaken at the request of the British Association. 



" We ought carefully to distinguish between that which appears 

 to be a direct inference from observed facts, and what at most can 



