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350 ORIGIN OF SPECIES 



Supposing B and C to be two species, and a third, A, to be 

 found in an older and underlying bed ; even if A were strictly 

 intermediate between B and C it would simply be ranked as a 

 third and distinct species, unless at the same time it could be 

 closely connected by intermediate varieties with either one or 

 both forms. Nor should it be forgotten, as before explained, 

 that A might be the actual progenitor of B and C, and yet 

 would not necessarily be strictly intermediate between them 

 r in all respects. So that we might obtain the parent-species 

 and its several modified descendants from the lower and 

 upper beds of the same formation, and unless we obtained 

 numerous transitional gradations, we should not recognise 

 their blood-relationship, and should consequently rank them 

 ^ distinct species. 



It is notorious on what excessively slight differences many 

 palaeontologists have founded their species; and they do this 

 the more readily if the specimens come from different sub- 

 stages of the same formation. Some experienced concholo- 

 gists are now sinking many of the very fine species of 

 D'Orbigny and others into the rank of varieties; and on this 

 view we do find the kind of evidence of change which on the 

 theory we ought to find. Look again at the later tertiary de- 

 posits, which include many shells believed by the majority of 

 naturalists to be identical with existing species ; but some ex- 

 cellent naturalists, as Agassiz and Pictet, maintain that all 

 these tertiary species are specifically distinct, though the dis- 

 tinction is admitted to be very slight; so that here, unless we 

 believe that these eminent naturalists have been misled by 

 their imaginations, and that these late tertiary species really 

 present no difference whatever from their living representa- 

 tives, or unless we admit, in opposition to the judgment of 

 most naturalists, that these tertiary species are all truly dis- 

 tinct from the recent, we have evidence of the frequent oc- 

 currence of slight modifications of the kind required. If we 

 look to rather wider intervals of time, namely, to distinct but 

 consecutive stages of the same great formation, we find that 

 the embedded fossils, though universally ranked as specific- 

 ally different, yet are far more Josely related to each other 

 than are the species found in more widely separated forma- 

 tions; so that here again we have undoubted evidence of 



