130 SIR CHARLES LYELL 



of which those mountains are composed have been formed, 

 some of them by igneous and others by aqueous action. 



It would be easy to multiply instances of similar uncon- 

 formability in formations of other ages; but a few more 

 will suffice. The carboniferous rocks before alluded to as 

 horizontal on the borders of Wales are vertical in the 

 Mendip hills in Somersetshire, where the overlying beds of 

 the New Red Sandstone are horizontal. Again, in the Wolds 

 of Yorkshire the last-mentioned sandstone supports on its 

 curved and inclined beds the horizontal Chalk. The Chalk 

 again is vertical on the flanks of the Pyrenees, and the ter- 

 tiary 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 

 winter and summer, although it has always been winter and 

 always summer in some part of the planet, and neither of 

 these seasons has ever reigned simultaneously over the 

 entire globe. They have been always shifting from place 

 to place ; but the vicissitudes which recur thus annually in 

 a single spot are never allowed to interfere with the inva- 

 riable 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 appearance of others on the globe, it will 

 then follow that the fossils of strata formed at two distant 

 periods on the same spot will differ even more certainly 

 than the mineral composition of those strata. For rocks of 

 the same kind have sometimes been reproduced in the same 

 district after a long interval of time; whereas all the evi- 

 dence derived from fossil remains is in favour of the opinion 

 that species which have once died out have never been 



