330 ABSEXTGB OF INTERMEDIATE VARIETIES 



than are the species found in more widely separated forma- 

 tions; so that here again we have undoubted evidence of 

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

 latter subject I shall return in the following chapter. 



With animals and j)Iants 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-form until they have 

 been modified and perfected in some considerable degree. 

 According to this view, the chance of discovering in a 

 formation in any one country all the early stages of transi- 

 tion 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 probable that 

 those which had the widest range, far exceeding the limits 

 of the known geological formations in Europe, have often- 

 est 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 modifica- 

 tion, though long as measured by years, was probably short 

 in comparison with that during which it remained without 

 undergoing 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, intermediate, fossil links, by asking our-' 

 selves 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 aboriginal stocks; or again, whether 



