316 



UNIFORMITY OF CHANGE. 



[Ch. XIV. 



It would be easy to multiply instances of similar uncon- 

 formability in formations of other ages ; but a few more will 

 suffice. The Coal-measures before alluded to as horizontal 



on the borders of Wales are vertical in 



Mendip Hills 



Somersetshire, where the overlying beds of the New Red 



Sandstone are horizontal. 



■s 



Wolds 



the last-mentioned sandstone supports on its curved and in- 

 clined beds the horizontal Chalk. The Chalk again is vertical 

 on the flanks of the Pyrenees, and the tertiary strata repose 

 unconformably upon it. 



As almost every country supplies illustrations of the same 

 phenomena, they who advocate the doctrine of alternate 

 periods of disorder and repose may appeal to the facts above 

 described, as proving that every district has been by turns 

 convulsed by earthquakes and then respited for ages from 

 convulsions. But so it might with equal truth be affirmed 

 that every part of Europe has been visited alternately by 



summer 



always 



summer 



globe. 



in some part of the planet, and neither of 

 isons has ever reigned simultaneously over the entire 

 They have been always shifting about from place to 

 place ; but the vicissitudes which recur thus annually in a 

 single spot are never allowed to interfere with the invariable 

 uniformity of seasons throughout the whole planet. 



So, in regard to subterranean movements, the theory of 

 the perpetual uniformity of the force which they exert on the 

 earth's crust is quite consistent with the admission of their 

 alternate development and suspension for long and indefi- 

 nite periods within limited geographical areas. 



If, for reasons before stated, we assume a continual extinc- 

 tion of species and introduction of others into the globe, it 

 will then follow that the fossils of strata formed at two dis- 

 tant periods on the same spot, will differ even more certainly 

 than the mineral composition of those strata. For rocks of 



same kind have sometimes 



time 



district after a long interval of 

 dence derived from fossil remains is in favour of the opinion 

 that species which have once died out have never been 

 reproduced. The submergence, then, of land must be often 



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