Natural History of Volcanos and Earthquakes. 231 



any trifling causes, lying near the surface, but that they are vast 

 and deeply-seated phenomena. Thus, for example, the whole 

 of the high country of Quito is one volcanic hearth, of which 

 the mountains of Pic/iincha, Cotopaxi, and Tunguragua^ form 

 the summits. The subterranean fire breaks out sometimes from 

 one, sometimes from another of these vents, which are usually 

 considered as distinct volcanos. The earthquakes, with which 

 America is so dreadfully visited, are also remarkable proofs of 

 the existence of subterranean communications, not only between 

 countries free from volcanos, as has been long known, but also 

 between volcanic hearths situated at a great distance from each 

 other. All these circumstances prove that the forces do not act 

 at the surface of the crust of the earth, but that, proceeding from 

 the interior of our planet, they communicate contemporaneously 

 by fissures with the most distant points on the surface.* 



Two hypotheses may be proposed respecting the causes of vol- 

 canic phenomena. The one supposes them to be occasioned by 

 intense chemical action taking place between bodies having a 

 very great affinity to each other, and by which so great a heat 

 is produced, that lavas melt and are forced to the surface of the 

 earth by the pressure of elastic flaids. According to the other, 

 the earth at a certain depth is at a white heat, and this heat is 

 the chief cause of volcanic phenomena. 



1. The hypothesis, which ascribes volcanic phenomena to intense 

 chemical action, sheivn to be untenable. 



We will not detain our readers, with an account of the earlier 

 hypotheses, which derive volcanic phenomena from the action of 

 iron upon sulphur, or from the combustion of pyrites or coal, as 

 their insufficiency is self-evident. But Davy's discovery of the 

 metallic bases of the alkalies and earths was considered as throw- 

 ing a great light on this subject. 



This distinguished philosopher, who instituted some very 

 interesting experiments at Vesuvius during its eruptions in 1814, 

 1815, 1819, and 1820, endeavored to explain the phenomena by 

 the oxidation of the metals of the alkalies and earths.f He 



* Von Humboldt's Reisen in die j^quinoctial Gegenden des neuen Continents, 

 t. i, p. 4R6, t. iii, p. 24, 26, and 40, offer many instances of this kind. 



t Sur les Phenomenes des Volcans. Annales de Chim. et de Phys. vol. xxxvii^ 

 p. 133. 



