ABSENCE OF INTERMEDIATE VARIETIES 351 



change in the direction required by the theory; but to this 

 latter subject I shall 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 formerly 

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

 such local varieties do not spread widely and supplant 

 their parent-forms until they have been modified and per- 

 fected in some considerable degree. According to this view, 

 the chance of discovering in a formation in any one country 

 all the early stages of transition between any two forms, is 

 small, for the successive changes are supposed to have been 

 local or confined to some one spot. Most marine animals 

 have, a wide range; and we have seen that with plants it is 

 those which have the widest range, that oftenest present va- 

 rieties ; so that, with shells and other marine animals, it is 

 probable that those which had the widest range, far exceed- 

 ing the limits of the known geological formations in Europe, 

 have oftenest given rise, first to local varieties and ultimately 

 to new species; and this again would greatly lessen the 

 chance of our being able to trace the stages of transition in 

 any one geological formation. 



It is a more important consideration, leading to the same 

 result, as lately insisted on by Dr. Falconer, namely, that the 

 period during which each species underwent modification, 

 though long as measured by years, w^as probably short in 

 comparison with that during which it remained without un- 

 dergoing any change. " 



It should not be forgotten, that at the present day, with 

 perfect specimens for examination, two forms can 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 perceive the improbability of our 

 being enabled to connect species by numerous, fine, inter- 

 mediate, fossil links, by asking ourselves whether, for in- 

 stance, 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 aboriginal 

 stocks; or, again, whether certain sea-shells inhabiting the 

 shores of North America, which are ranked by some con- 



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