270 ON THE ORIGIN OF SPECIES 



such gradations were not fully preserved, transitional 

 varieties would merely appear as so many distinct 

 species. It is, also, probable that each great period 

 of subsidence would be interrupted by oscillations of 

 level, and that slight climatal changes would intervene 

 during such lengthy periods ; and in these cases the 

 inhabitants of the archipelago would have to migrate, 

 and no closely consecutive record of their modifications 

 could be preserved in any one formation. 



Very many of the marine inhabitants of the archi- 

 pelago now range thousands of miles beyond its con- 

 fines ; and analogy leads me to believe that it would be 

 chiefly these far-ranging species which would oftenest 

 produce new varieties ; and the varieties would at first 

 generally be local or confined to one place, but if 

 possessed 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, they would, accord- 

 ing 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 formations, an infinite number of those fine 

 transitional forms, which on my theory assuredly have 

 connected all the past and present species of the same 

 group into one long and branching chain of life. We 

 ought only to look for a few links, some more closely, 

 some more distantly related to each other ; and these 

 links, let them be ever so close, if found in different 

 stages of the same formation, would, by most palaeonto- 

 logists, be ranked as distinct species. But I do not 

 pretend that I should ever have suspected how poor 

 a record of the mutations of life, the best preserved 

 geological section presented, had not the difficulty of our 

 not discovering innumerable transitional links between 

 the species which appeared at the commencement and 

 close of each formation, pressed so hardly on my theory. 



