A HISTORY OF SCIENCE 



back again. But if this be the real significance of the 

 seemingly sudden change from stratum to stratum, 

 then the whole case for catastrophism is hopelessly lost ; 

 for such breaks in the strata furnish the only suggestion 

 geology can offer of sudden and catastrophic changes 

 of wide extent. 



Let us see how Lyell elaborates these ideas, particu- 

 larly with reference to the rotation of species. * 



" I have deduced as a corollary," he says, " that the 

 species existing at any particular period must, in the 

 course of ages, become extinct, one after the other. 

 1 They must die out,' to borrow an emphatic expression 

 from Buffon, ' because Time fights against them. * If the 

 views which I have taken are just, there will be no diffi- 

 culty in explaining why the habitations of so many 

 species are now restrained within exceeding narrow 

 limits. Every local revolution tends to circumscribe 

 the range of some species, while it enlarges that of 

 others ; and if we are led to infer that new species orig- 

 inate in one spot only, each must require time to diffuse 

 itself over a wide area. It will follow, therefore, from 

 the adoption of our hypothesis that the recent origin 

 of some species and the high antiquity of others are 

 equally consistent with the general fact of their limited 

 distribution, some being local because they have not 

 existed long enough to admit of their wide dissemina- 

 tion; others, because circumstances in the animate or 

 inanimate world have occurred to restrict the range 

 within which they may once have obtained. . . . 



" If the reader should infer, from the facts laid before 

 him, that the successive extinction of animals and 

 plants may be part of the constant and regular course 



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