Chap. XL] PRECEDING AND PRESENT CHAPimS. 125 



although each species must have passed through nuimer- 

 ous transitional stages, it is probable that the period 

 during which each underwent modification, though" 

 many and long as measured by years, have been short 

 in comparison with the periods during which each re- 

 mained in an unchanged condition. These causes, 

 taken conjointly, will to a large extent explain why — 

 though we do find many links — we do not find inter- 

 minable varieties, connecting together all extinct and 

 existing forms by the finest graduated steps. It should 



^algoJie.^constantly borne in noind that any linking va- 

 riety between two forms, which might be'fbund, would 

 '~T)e ranFe'd, unless the whole chain could be perfectly 

 restored, as a new and distiiict species; for it_is not pre- 



/teintedthat we have any sure criterion by which species 

 and varieties can be discriminated. 



IIe~who rejects this view of the imperfection of the 

 geological record, will rightly reject the whole theory. 

 For he may ask in vain where are the numberless tran- 

 sitional links which must formerly have connected the 

 closely allied or representative species, found in the 

 successive stages pf the same great formation? He 

 may disbelieve in the immense intervals of time which 

 must have elapsed between our consecutive formations; 

 he may overlook how important a part migration has 

 played, when the formations of any one great region, 

 as those of Europe, are considered; he may urge the 

 apparent, but often falsely apparent, sudden coming in 

 of whole groups of species. He may ask where are the 

 remains of those infinitely numerous organisms which 

 must have existed long before the Cambrian system 

 was deposited? We now know that at least one animal 

 did then exist; but I can answer this last question only 



