282 ABSENCE OF INTERMEDIATE VAEIETIP:S Chap. IX. 



several modified descendants from tlu^ lower and upper beds of 

 the same formation, and unless "\ve obtained numerous transi- 

 tional gradations, we should not reco^ize their blood-relation- 

 ship, and should consequently be compelled to rank them as 

 distinct species. 



It is notorious on what excessively slight differences many 

 paleontologists liave founded their species; and they do this 

 the more readily if the specimens come from different sub- 

 stages of the same formation. Some experienced conchologists 

 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 tlie theory we 

 ought to find. Look, again, at the later tertiary deposits, 

 which include many shells believed by the majority of natural- 

 ists to be identical with existing species ; but some excellent 

 naturalists, as Agassiz and Pictet, maintain that all these ter- 

 tiary species are specifically distinct, though the distinction 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 representatives, or unless we believe 

 that the great majority of naturalists are wrong, and that the 

 tertiar}' sjiecies are all truly distinct from the recent, we have 

 evidence of the frequent occurrence of sliglit 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 almost 

 universally ranked as specifically different, yet are far more 

 closely related to each other than are the species found in more 

 widely-separated formations ; so that here again we have un- 

 doubted evidence of change in the direction required by the 

 theory ; but to this latter subject I shall have to return in the 

 following chapter. 



With animals and plants that propagate rapidly and do 

 not wander much, there is reason to suspect, as we have for- 

 merly seen, that their varieties are generally at first local ; and 

 that such local varieties do not spread widely and supplant 

 their parent-forms imtil they have been modified and perfected 

 in some considerable degree. According to this A'icw, the 

 chance of discovering in a fonnation in any one country all the 

 early stages of transition between any two such forms is small, 

 for the successive changes are supposed to liave been local, or 

 confined to some one spot. Most marine animals have a wide 



