Chap. XL] AFFINITIES OF EXTINCT SPECIES. 115 



the globe, will not attempt to account for the close re- 

 semblance of distinct species in closely consecutive for- 

 mations, by the physical conditions of the ancient areas 

 having remained nearly the same. Let it be remembered 

 that the forms of life, at least those inhabiting the sea, 

 have changed almost simultaneously throughout the 

 world, and therefore under the most different climates 

 and conditions. Consider the prodigious vicissitudes of 

 climate during the pleistocene period, which includes 

 the whole glacial epoch, and note how little the specific 

 forms of the inhabitants of the sea have been affected. 



On the theory of descent, the full meaning of the 

 fossil remains from closely consecutive formations be- 

 ing closely related, though ranked as distinct species, is 

 obvious. As the accumulation of each formation has 

 often been interrupted, and as long blank intervals have 

 intervened between successive formations, we ought not 

 to expect to find, as I attempted to show in the last 

 chapter, in any one or in any two formations, all the in- 

 termediate varieties between the species which appeared 

 at the commencement and close of these periods: but 

 we ought to find after intervals, very long as measured 

 by years, but only moderately long as measured geologi- 

 cally, closely allied forms, or, as they have been called 

 by some authors, representative species; and these as- 

 suredly we do find. We find, in short, such evidence of 

 the slow and scarcely sensible mutations of specific 

 forms, as we have the right to expect. 



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