99 NATURAL HISTORY. , 



the inflammation cannot be supported without air. In 

 order to be convinced that the matter emitted by volca~ 

 njes does riot come from any considerable depth, we 

 have only to attend to the height of the mountain, ancV 

 ta consider th amazing force which would be necessary 

 to project, stones and minerals to the height of half a 

 league ; for JEtna, Hecla, and other volcanoes, have at 

 least that elevation. 



This, however, is not inconsistent with volcanoes 

 being the cause of considerable earthquakes ; nor does 

 it contradict, the communication of one volcano with 

 another, by means of subterraneous passages, For 

 to produce an earthquake in a plain, it is not necessary 

 that the bottom of the volcano should be below the le- 

 vel of that plain, nor that there should be subterraneous- 

 cavities filled with the same burning matter under it. 

 A violent explosion may by its reaction produce an 

 earthquake of considerable extent. I would not, how- 

 ever, be thought to say that no earthquakes derive 

 their existence from subterraneous fires ; all I mean is, 

 that there are earthquakes produced solely by the ex- 

 plosion of volcanoes. 



It is not dii'iicult to account for volcanoes appearing 

 only in mountains ; for greater quantities of minerals, 

 sulphur, and pyrites, exist in mountains, and nearer 

 the surface than in the plains. Besides, mountains are 

 more subject to the impressions of the air, and receive 

 more rain and moisture, by which mineral substances 

 are capable of being fermented to such a degree as to 

 produce actual inflammation. And mountains having 

 diminished, nearly in proportion to the quantity of mat- 

 ter thrown out, is another proof that the volcanoes are 

 not so deep as the base of the mountains, and even that 

 they are not much below the summit. 



