298 IMPEKFECTION OF THE Chap. IX. 



yet are far more closely allied to each other than 

 are the species found in more widely separated forma- 

 tions ; but to this subject I shall have to return in the 

 following chapter. 



One other consideration is worth notice : with animals 

 and plants that can propagate rapidly and are not 

 highly locomotive, 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 perfected in some considerable de- 

 gree. 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 

 varieties ; so that with shells and other marine animals, 

 it is probably those which have had the widest range, 

 far exceeding the limits of the known geological forma- 

 tions of Europe, which 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 geo- 

 logical formation. 



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 

 have been collected from many places ; and in the case 

 of fossil species this could rarely be effected by palae- 

 ontologists. We shall, perhaps, best perceive the im- 

 probability of our being enabled to connect species by 

 numerous, fine, intermediate, fossil links, by asking 



