Ch. XXIV.] OF MOUNTAIN-CHAINS. 339 



be referred to ordinary volcanic forces, but may depend on the 

 secular refrigeration of the heated interior of our planet*.' 



It will at once be seen, that the greater number of the above 

 propositions are directly opposed to that theory which we have 

 endeavoured to deduce, partly from the study of the earth's 

 structure, and partly from the analogy of changes now in pro- 

 gress in the animate and inanimate world. 



Our opinions respecting the alternation of periods of general 

 repose and disorder have been explained in former chapters f ; 

 and we have pointed out our objections to the hypothesis 

 which substitutes paroxysmal violence for the reiterated recur- 

 rence of minor convulsions J. 



The speculation of M. de Beaumont concerning the ' secular 

 refrigeration' of the internal nucleus of the globe, considered as 

 a cause of the instantaneous rise of mountain-chains, appears to 

 us mysterious in the extreme, and not founded upon any in- 

 duction from facts; whereas the intermittent action of sub- 

 terranean volcanic heat is a known cause capable of giving rise 

 to the elevation and subsidence of the earth's crust without 

 interruption to the general repose of the habitable surface. 



We have shown, in the second volume, that we believe the 

 changes in physical geography, which are unceasingly in pro- 

 gress, to be among the causes which contribute, in the course 

 of ages, to the extermination of certain species of animals and 

 plants ; but the influence of these causes is slow and, for the 

 most part, indirect, and has no analogy with those sudden 

 catastrophes which are introduced into the theory now under 

 review. What have appeared to us to be the true causes of 

 the abrupt transitions from one set of strata to another, con- 

 taining distinct organic remains, have been explained at length 

 in the third and fourth chapters of this volume^. 



* Ann. des Sci. Nat., Septembre, Novembre, et De"cembre, 1829. Revue 

 Franqaise, No. 15, May, 1830. The last version by M. de B. which I have 

 seen is in the Phil. Mag. and Annals, No. 58, new series, p. 241. 



f Vol. i. pp. 64 and 88, and Second Edition, pp. 73 and 100; vol. ii. p. 196, 

 and Second Edition, p. 203. 



J Vol. i, p. 79, and Second Edition, p. 90. 



See particularly from p. 26 to p, 34. 



Z 2 



