the Revolutions which have taken i^lace on the Globe. 263 



in different directions ; the mind would not rest satisfied if it 

 did not perceive, among those causes now in action, an ele- 

 ment fitted from time to time to produce disturbances dif- 

 ferent from the ordinary march of the phagnomena which we 

 now witness. 



The idea of volcanic action naturally presents itself when 

 we search, in the existing state of things, for a term of com- 

 parison with these great pheenomena. They nevertheless do 

 not appear susceptible of being referred to volcanic action, 

 unless we define it, with M. Humboldt, as being the injluence 

 exercised by the interior of a planet on its exterior covering 

 during its diffei-ent stages (f refrigeration. 



Volcanos are frequently arranged in lines following frac- 

 tures parallel to mountain-chains, and which originate in the 

 elevation of such chains ; but it does not appear to me that 

 we can thence regard the elevation of the chains themselves as 

 due to the action of volcanic foci, taking the words in their 

 ordinary and restricted sense. We can easily conceive how 

 a volcanic focus may produce accidents circularly and in the 

 form of rays from a centi'al point, but we cannot conceive how 

 even many unitedybcz could produce those ridges which follow 

 a common direction through several degrees. 



Volcanic action, such as it is commonly understood, could 

 not therefore be itself the first cause of these great pbseno- 

 mena ; but volcanic action appears to be related (and this is 

 a subject which has long occupied M. Cordier, though he has 

 considered it under another point of view) with the high tem- 

 perature now existing in the earth. 



Now the secular refrigeration, that is to say, the slow dif- 

 fusion of the primitive heat to which the planets owe their 

 spheroidal form, and the generally regular disposition of their 

 beds from the centre to the circumference, in the order of 

 specific gravity, — the secular refrigeration, on the march of 

 which M. Fourier has thrown so much light, does offer an 

 element to which these extraordinary effects may be referred. 

 This element is the relation which a refrigeration so advanced 

 as that of the planetary bodies establishes between the capa- 

 city of their solid crusts and the volume of their internal 

 masses. In a given time, the temperature of the interior of 

 the planets is lowered by a much greater quantity than that on 

 their surfaces, of which the refrigeration is now nearly insen- 

 sible. We are, undoubtedly, ignorant of the physical pro- 

 perties of the matter composing the interior of these bodies; 

 but analogy leads us to consider, that the inequality of cooling 

 above noticed would place their crusts under the necessity of 



continually 



