UliPOUT ON MINKKAL AXD THERMAL WATKRS. G9 



would be afforded, by the supposed oxidation of the bases, of 

 those alkalis, earths, and metallic oxides, which are found to 

 constitute the crust of the globe, through the agency, first of 

 Mater, and afterwards of atmospheric air. 



Such, in a few words, was the theory which I adopted, to 

 account for the phaenomenaof volcanos* in a work published on 

 that subject in 1826t ; and to the same, after a mature, and, I 

 trust, an impartial review of the question, I am still disposed to 

 adhere, in preference at least to any other. 



In an article entitled Geology, in the Encyclopedia Metro- 

 politana, I have endeavoured to reply to all the arguments that 

 had been subsequently urged against my views ; and if I have not 

 noticed every individual objection, it has only been, because 

 the same difficulties were brought forvvai-d again and again by 

 different persons, often without any allusion being made to the 

 answers, which I had given to similar ones before. 



The latter theory, discarding all chemical operations whatso- Theory of 

 ever, regards thermal springs as arising merely from the internal central 

 heat of the globe, and consequently as possessing a temperature 

 high, in proportion to the depth from which thej' have themselves 

 proceeded. 



For, as the temperature of the earth augments, as we descend, 

 on the average, about I'^of Fahr. for every 100 feet, it is evident, 

 that, if the increase be progressive, water would arrive at its 

 boiling point at a depth not exceeding three miles, and there is 

 no difficulty in understanding, that it should retain the greater 

 part of that exalted temperature, when once the channels and 

 passages in the rock, through which it reached the surface, were 

 thoroughly penetrated by the heat. 



The theory just mentioned is sanctioned by the high autho- 



eye-witness of another Phlegethon discharging itself into the bowels of the 

 earth, in every volcanic district, as in the solitary case of Cephalonia. 



Nor, as I shall afterwards attempt to prove, is the access of atmospheric 

 air to volcanos more questionable, than that of water ; so that the appearance, 

 of hydrogen united with sulphur, and of nitrogen, either alone, or combined 

 with hydrogen, at the mouth of the volcano, seems a direct proof, that oxygen 

 has been abstracted by some process or other from both. 



Having satisfied our minds with regard to the fact of internal oxidation, 

 we naturally turn to consider, what principles can have existed in the inte- 

 rior of the earth, capable of abstracting oxygen from water, as well as from 

 air; and this leads us to speculate on the bases of the earths and alkalis as 



I having caused it. But in ascribing the pheenomena to the oxidation of these 

 bodies, we ought not to lose sight of the Baconian maxim, that in every well- 

 established theory, the cause assigned should be, not only competent to explain 

 the phaenomena, but also known to have a real existence, which latter cannot 

 be predicated of my alkaline and earthy metalloids in the interior of the 

 earth. 

 * Description nf Active and Extinct Volcanos. London, 1826. 

 I 



