Chap. XL] PEECEDING AND PEESENT CHAPTEES. 125 



must have passed through numerous transitional stages, 

 it is probable that the periods, during which each 

 underwent modification, though many and long as 

 measured by years, have been short in comparison with 

 the periods during which each remained 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 interminable varieties, connecting together all 

 extinct and existing forms by the finest graduated steps. 

 It should also be constantly borne in mind that any 

 linking variety between two forms, which might be found, 

 would be ranked, unless the whole chain could be 

 perfectly restored, as a new and distinct species ; for it 

 is not pretended that we have any sure criterion by which 

 species and varieties can be discriminated. 



He 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 

 transitional links which must formerly have connected 

 the closely allied or representative species, found in 

 the successive stages of 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 by supposing that where our oceans now extend 



