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 Pichincha, Cotopazi, 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 
tween 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.* 
Wo 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 fluids. 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. 
: The hypothesis, which ascribes volcanic phenomena to intense 
chemical action, shewn to be untenable. 
We will not detain our readers, with an account of the earlier 
‘ypotheses, which derive volcanic phenomena from the action of 
ton 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- 
iN 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.+ He 
ge ee oer rea oN 
*Von Humboldt’s Reisen in die ZEquinoctial Gegenden des neuen Continents, 
*4,p. 496, t. iii, p. 24, 26, and 40, offer many instances of this kind. . 
p mg es Phenomenes des Volcans. Annales de Chim, et de Phys. vol. xxxvii, 
