

576 



IGNEOUS CAUSES. 



[Ch. XXIII. 



sea, cannot destroy coasts, shape out or silt up estuaries, 

 break through isthmuses, and annihilate islands, form shoals 

 in one place, and remove them from another, without the direc- 

 tion and position of their destroying and transporting power 

 becoming transferred to new localities. Neither can the 

 relative levels of the earth's crust, above and beneath the 

 waters, vary from time to time, as they are admitted to have 

 varied at former periods, and as it will be demonstrated that 

 they still do, without the continents being, in the course of 

 ages, modified, and even entirely altered, in their external 

 configuration. Such events must clearly be accompanied by 

 a complete change in the volume, velocity, and direction of 



the streams and land floods to which certain regions 



give 



passage, 

 sea once 



That we should find, therefore, cliffs where the 

 committed ravages, 



and 



om 



retired — estuaries where high tides once rose, but which are 

 now dried up — valleys hollowed out by water, where no 



than we should exnect ; — these 



more 



and 



omena 



are the necessary consequences of 

 physical causes now in operation ; and if there be no insta- 

 bility in the laws of nature, similar fluctuations must recur 



again and again in time to come. 



m 



numerous 



tracts of the sea, should now be spent, it is by no means so 

 easy to explain why the violence of the earthquake and the 

 fire of the volcano should also have become locally extinct at 

 successive periods. "We can look back to the time when the 

 marine strata, whereon the great mass of Etna rests, had no 

 existence ; and that time is extremely modern in the earth's 

 history. This alone affords ground for anticipating that the 

 eruptions of Etna will one day cease. 



Nee quse sulfureis ardet fornacitras iEtna 

 Ignea semper erit, neque enimfuit ignca semper, 



(Ovid, Mdam. lib. 15—3-10.) 







9 



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an' 





rthqi 







<y>i. 





% 



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4 



memorable 



Pythagoras by the Soman poet, and they are followed by 

 speculations as to the cause of volcanic vents shifting their 













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