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Ch. XXXII. 1 THE EAETH'S CENTEAL FLUIDITY QUESTIONED 



211 



times, but that they have never been the theatres of such 

 action at any subsequent epoch. On the other hand, we 

 often find that regions w^here showers of volcanic ashes and 



e 



matter 



frequent, are now entirely free from volcanic disturbance. 

 The continual transfer, therefore, of the points of chief 

 development of the earthquake and volcano from one part 

 of the earth's crust to another, is established as a general 



law bj the clearest geological evidence. We have also seen 

 (Chapter XXIII.) that volcanic operations are now in progress 

 on the grandest scale, and also that single currents of lava of 

 modern date are as voluminous as any which can be shown 

 to have ever poured out in the earliest eras to which our 

 geological retrospect can be carried. 



The doctrine, therefore, of the pristine fluidity of the interior 

 of the earth, and the gradual solidification of its crust con- 

 sequent on the loss of internal heat by radiation into space, 

 is one of many scientific hypotheses, which has been adhered 

 to after the props by which it was at first supported have given 

 way one after the other. The astronomer may find good reasons 

 for ascribing the earth's form to the original fluidity of the 



must 



regard the earliest monuments which it is his task to inter- 

 pret as belonging to a period when the crust had already 

 acquired great solidity and thickness, probably as great as 

 it now possesses, and when volcanic rocks not essentially dif- 

 fering from those now produced were formed from time to 

 time, the intensity of volcanic heat being neither greater 



noT^ 



This lieat lias, no doubt, given 



rise 



at successive periods to many of the leading changes in the 



form 



means 



. ^ — ^^^xg i,iic Igneous 



lusion ot the whole planet to account for them If the 

 reader will refer to the diagram, fig. 128, p. 212 * he mav 

 convince himself that a machinery more utterly disproportion- 

 ate to the effects which it is required to explain was never 

 appealed to. The outer circular line of the diagram renre 



miles 



P 2 



