Chap. IX. GEOLOGICAL KECORD. 301 



indispensable for the preservation of all the transitional 

 gradations between any two or more species. If 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 archi- 

 pelago would have to migrate, and no closely consecu- 

 tive record of their modifications could be preserved in 

 any one formation. 



Very many of the marine inhabitants of the archipe- 

 lago now range thousands of miles beyond its confines ; 

 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 gene- 

 rally 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, 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 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- 



