2i2 Dr Charles Daubeny on (he 



For, granting that no other of the bases which enter into 

 the composition of lava would inflame on the approach of 

 water, the metals of the alkalies, at least, which constitute 

 sometimes as much as one-tenth of the entire bulk of the 

 ejected matter, would certainly do so, whence must result a 

 considerable evolution of hydrogen, and a generation of heat 

 sufficient to cause all the unoxidized substances in the vicinity 

 to unite with the oxygen presented to them. 



But, without entering into a complete exposition of this 

 theory, I think it must on all hands be admitted, that if its 

 relative merits are to be decided by its capability of explain- 

 ing the phenomena, it may fairly claim the preference over 

 the rival hypothesis. 



If, indeed, we assume that the globe was once fluid, and 

 take for granted that it still retains a sufficiently high tem- 

 perature to preserve its original fluidity in the interior (al- 

 though the slight depth to which we have yet penetrated 

 hardly justifies us in speaking decisively as to the state of 

 things which may exist below a certain depth), there is even 

 then but one phenomenon of volcanic action, which, so far 

 as I know, can be fairly deduced from these premises, namely, 

 the protrusion in certain localities of melted matter from the 

 surface. For the ejection of fragments of rocks, the evolu- 

 tion of steam, and the disengagement of various gaseous com- 

 pounds, are phenomena of which this hypothesis seems to give 

 no account. Nor does it seem clear, why the lines of least 

 resistance should be found almost invariably near the sea, or 

 why, indeed, they should occur at all underneath the bed of 

 an ocean, where the controlling pressure must be even greater 

 than it is in the midst of our continents. 



Accordingly, most of those persons who profess to hold to 

 the theory of central heat, in reality combine with it some 

 hypothesis into which chemical considerations enter. 



They explain, for instance, the evolution of steam, and of 

 muriatic acid, by the access of salt water to the spots where 

 this melted matter is supposed to exist, by the chemical ac- 

 tion of which the muriatic acid is separated from its base, 

 and the water converted into steam. 



