2i6 CLASSICS OF MODERN SCIENCE 

 in formations of other ages ; but a few more will suffice. The carbon- 

 iferous 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 tertiary strata repose unconformably 

 upon it. 



As almost every country supplies illustrations of the same phe- 

 nomena, they who advocate the doctrine of alternate periods of dis- 

 order 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 

 invariable uniformity of seasons throughout the whole planet. 



So, in regard to subterranean movements, the theory of the per- 

 petual 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 indefinite periods within limited geographical 

 areas. 



If, for reasons before stated, we assume a continual extinction 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 dififer 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 reproduced. The 

 submergence, then, of land must be often attended by the commence- 

 ment of a new class of sedimentary deposits, characterized by a new 

 set of fossil animals and plants, while the reconversion of the bed of 

 the sea into land may arrest at once and for an indefinite time the 

 formation of geological monuments. Should the land again sink, 



