312 ABSENCE OF INTERMEDIATE VARIETIES 



extinction of life ; during the periods of elevation, there 

 would be much variation, but the geological record would 

 then be less perfect. 



It may be doubted whether the duration of any one great 

 period of subsidence over the whole or part of the archi- 

 pelago, together with a contemporaneous accumulation of 

 sediment, would exceed the average duration of the same 

 specific forms ; and these contingencies are indispensable 

 for the preservation of all the transitional gradations between 

 any two or more species. If such gradations were not all 

 fully preserved, transitional varieties would merely appear 

 as so many new, though closely allied species. It is also 

 probable that each great period of subsidence would be inter- 

 rupted by oscillations of level, and that slight climatical 

 changes would intervene during such lengthy periods ; and 

 in these cases the inhabitants of the archipelago would 

 migrate, and no closely consecutive record of their modifica- 

 tions could be preserved in any one formation. 



Very many of the marine inhabitants of the archipelago 

 now range thousands of miles beyond its confines ; and 

 analogy plainly leads to the belief that it would be chiefly 

 these far-ranging species, though only some of them, which 

 would oftenest produce new varieties ; and the varieties 

 would at first be local or confined to one place, but if pos- 

 sessed of any decided advantage, or when further modified 

 and improved, they would slowly spread and supplant their 

 parent forms. When such varieties returned to their ancient 

 homes, as they would differ from their former state in a 

 nearly uniform, though perhaps extremely slight degree, and 

 as they would be found embedded in slightly different sub- 

 stages of the same formation, they would, according to the 

 principles followed by many palaeontologists, be ranked as 

 new and distinct species. 



If then there be some degree of truth in these remarks, 

 we have no right to expect to find, in our geological forma- 

 tions, an infinite number of those fine transitional forms 

 which, on our theory, have connected all the past and pres- 

 ent species of the same group into one long and branching 

 chain of life. We ought only to look for a few links, and 

 such assuredly we do find — some more distantly, some more 

 closely, related to each other; and these links, let them be 

 ever so close, if found in different stages of the same forma- 

 tion, would, by many palaeontologists, be ranked as distinct 

 species, But I do not pretend that I should ever have. 



