204 Effects of Heat modified I y Compression* 



of volcanoes. It is no less obvious, that the temperature of 

 that liquid must be of far greater intensity than the lavas, 

 flowinti from it, can retain when they reach the surface. 

 Independently of anv actual eruption, the body of heat con- 

 tained in this vast mass of liquid must diffuse itself through 

 the surrounding substances, the intensity of the heat being 

 diminished bv slow gradations, in proportion to the distance 

 to which it penetrates. When, by means of this progres- 

 sive diffusion, the heat has reached an assemblage of loose 

 marine deposites, subject to the pressure of a great superin- 

 cumbent weight, the whole must be agglutinated into a 

 mass, the solidity of which will vary with the chemical 

 composition of the substance, and with the degree of heat 

 to which each particular spot has thus been exposed. At 

 the same time, analogy leads us to suppose that this deep 

 and extensive heat must be subject to vicissitudes and inter- 

 missions like the external phaenomena of volcanoes. We 

 have endeavoured to explain some of these irregularities, 

 and a similar reasoning may be extended to the present case. 

 Having shown that small internal streams of lava tend suc- 

 cessively to pervade every weak part of a volcanic mountain, 

 we are led to conceive that the great masses of heated matter 

 just mentioned will be successively directed to different parts 

 of the earth ; so that every loose assemblage of matter lying 

 in a submarine and subterranean situation, will, in its turn, 

 be affected by the indurating cause, and the influence of in- 

 ternal volcanic heat will thus be circumscribed within no 

 limits but those of the globe itself. 



A series of undoubted facts prove that all our strata once 

 lay in a situation similar in all respects to that in which the 

 marine deposites just mentioned have been supposed to lie. 



The inhabitant of an unbroken plain, or of a country 

 formed of horizontal strata, whose observations have been 

 confined to his na'ive spot, can form no idea of thct;'. truths 

 which at everv step, in an alpine district, force themselves 

 on the mind of a geological observer. Unfortunately for the 

 progress of gcologv, both London and Paris are placed in 

 countries of little interest ; and those scenes by which the 

 principles of this science are brought into view in the most 



striking: 



