M. Gay Lussac’s Reflections on Volcanoes. 279 
to certain questions connected with chemistry, and for which it 
is not requisite to possess all the information necessary to con- 
stitute a geologist. The subject is besides a difficult one, and 
requires indulgence. 
Two hypotheses may be formed regarding the cause by which 
the phenomena of volcanoes are produced. According to one 
of these, the earth is still in a state of incandescence at a cer- 
tain depth below its surface, as the observations recently made 
in mines upon the augmentation of its temperature would lead 
us to presume ; and this heat is the principal cause of volcanic 
phenomena. According to the other hypothesis, their princi- 
pal cause is a very energetic affinity between substances, for- 
tuitously brought into contact with each other, and from which 
results a heat sufficient for melting lavas, and raising them by 
the pressure of elastic fluids to the surface of the earth. 
Both hypotheses have this in common, that the volcanic fires 
must necessarily be fed by substances which were at first foreign 
to them, and which are carried to them in some manner or other. 
In fact, at those remote periods which have witnessed the great 
catastrophes of our globe, periods at which its temperature must 
have been more elevated than at the present day, and the melted 
matters which it contained consequently more liquid, the resist- 
ance of its surface less, and the pressures exercised by the elastic 
fluids greater, all that could be produced has been done ; an 
equilibrium must have been established, a state of repose which 
could no longer be interrupted by intestine causes, and which 
could only be so in our times by new contacts between bodies, 
which are brought together by accidental causes, and which 
perhaps have only been added to the mass of the globe poste- 
riorly to the solidification of its surface. 
Now, the possibility of bodies finding their way from the sur- 
face to the interior of the earth, the ascent of lavas to considerable 
heights above the surface of the earth, the ejections by explosion, 
and earthquakes, necessarily require that the foreign substances 
which penetrate into the volcanic foci be elastic fluids, or rather 
liquids capable of producing them, either by heat, which reduces 
them to a state of vapour, or by affinity, which disengages some 
gaseous elements. 
On consulting analogy, w 7 e find, that the substances Capable 
