278 Remarks on Volcanoes. 



other Phlegethon, discharging itself into the bowels of the 

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

 Cephalonia. 



4< Nor is the access of atmospheric air 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 in- 

 ternal oxidation, we naturally turn to consider what prin- 

 ciples can have existed in the interior of the earth capable of 

 abstracting oxygen from water, as well as from air ; and this 

 leads us to speculate on the basis of the earths and alkalies, 

 as having been instrumental in causing it. But in ascribing 

 the phenomena 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 facts, but also known to have a real 

 existence^ which latter circumstance cannot, of course, be 

 affirmed of the alkaline and earthy metalloids, as having a 

 place in the interior of the earth." 



I should not despair of being able to shew that such an 

 hypothesis is still tenable ; but it will be more profitable on 

 the present occasion, as well as, I doubt not, more agreeable 

 to my hearers, for me to point out the substantial additions 

 which Professor Bunsen has supplied to our knowledge of this 

 class of phenomena. 



He has, in the first place, proved that the products of 

 volcanic action — at least as they display themselves in that- 

 vast focus of internal energy which we observe in the island 

 of Iceland — consist only of two kinds of material : either 

 a trachytic rock, consisting of a trisilicate of alumina, con- 

 joined with a similar compound of silica, with an alkali 

 or alkaline earth ; or else an augite rock, in which one 

 atom, only, of silica, is combined with two atoms either of 

 alumina, protoxide of iron, lime, magnesia, potass, or soda. 



Bunsen has given a formula by which the proportion be- 

 tween these two constituents in any given rock may be readily 



