Chap.X.] in any single FORMATION. 73 



seldom be connected by intermediate varieties, and thus 

 proved to be the same species, until many specimens 

 are collected from many places; and with fossil species 

 this can rarely be done. We shall, perhaps, best per- 

 ceive the improbability of our being enabled to con- 

 nect species by numerous, fine, intermediate, fossil links, 

 by asking ourselves whether, for instance, geologists 

 at some future period will be able to prove that our 

 different breeds of cattle, sheep, horses, and dogs are 

 descended from a single stock or from several abori- 

 ginal stocks; or, again, whether certain sea-shells in- 

 habiting the shores of North America, which are 

 ranked by some conchologists as distinct species from 

 their European representatives, and by other con- 

 chologists as only varieties, are really varieties, or 

 are, as it is called, specifically distinct. This could 

 be effected by the future geologist only by his discover- 

 ing in a fossil state numerous intermediate grada- 

 tions; and such success is improbable in the highest de- 

 gree. 



It has been asserted over and over again, by writers 

 who believe in the immutability of species, that geology 

 yields no linking forms. This assertion, as we shall 

 see in the next chapter, is certainly erroneous. As Sir 

 J. Lubbock has remarked, " Every species is a link 

 "between other allied forms." If we take a genug 

 having a score of species, recent and extinct, and de- 

 stroy four-fifths of them, no one doubts that the re- 

 mainder will stand much more distinct from each other. 

 If the extreme forms in the genus happen to have been 

 thus destroyed, the genus itself will stand more distinct 

 from other allied genera. What geological research 

 has not revealed, is the former existence of infinitely 



