Masterpieces of Science 



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 in- 

 variable 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 in- 

 definite periods within limited geographical 

 areas. 



If, for reasons before stated, we assume a con- 

 tinual 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 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 in- 

 terval of time; whereas all the evidence derived 

 from fossil remains is in favour of the opinion 

 that species that 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 in- 

 definite time the formation of geological monu- 

 ments. Should the land again sink, strata will 

 again be formed; but one or many entire revolu- 

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