372 ON VOLCANOES AND EARTHQUAKES. 



sumed, attended by a proportionate disengagement of 

 hydrogen, which is not now in existence. 



The last hypothesis is that which supposes the per- 

 petual existence of a central fire, or heat, ready to 

 produce inflammation and its consequences, whether 

 from the admission of water, or from internal che- 

 mical actions occurring in consequence of changes 

 respecting which we cannot, at present, easily spe- 

 culate. As this doctrine forms also the basis of the 

 hypothesis which relates to the unstratified rocks, it 

 connects, by one common cause, those things which 

 are so exactly connected in their natures and appear- 

 ances. The permanence of this central heat is indi- 

 cated by the permanence of volcanic fires, and by the 

 phenomena of hot springs. The force exerted may 

 be the consequence of the changes already mentioned, 

 or of an expansion, the nature of which has not been 

 explained. It is plain, that as far as the excitement 

 of the action by water is concerned, it does not labour 

 under the same difficulties as the last ; as it is not 

 necessary that the water should be decomposed, and 

 as the supposed expansion might produce, at irregular 

 intervals, those fissures which are necessary for its 

 transmission. The objections which have been made 

 to this theory are of no force, as far as relates to its 

 power, its properties, or its modifications ; and by 

 adding some not unreasonable assumptions, it is easy 

 to modify it to all the requisite ends. It is but one 

 portion of that general theory which includes the 

 causes of the figure of the earth and of all its impor- 

 tant revolutions ; of which also, the phenomena of 

 volcanoes form one of the leading evidences. 



It assuredly presents a more magnificent and con- 

 sistent view of nature, to consider Volcanoes as parts 

 of one great system, and not as casual and partial 



