THE IMPERFECTION OF THE GEOLOGICAL RECORD 287 



periods of subsidence, there would probably be much extinction 

 of life; during the periods of elevation, there would be much var- 

 iation, but the geological record would then be less perfect. 



It may be doubted whether the duration of any one great pe- 

 riod of subsidence over the whole or part of the archipelago, to- 

 gether 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 interrupted by oscillations of level, and that slight 

 cHmatical changes would intervene during such lengthy periods; 

 and in these cases the inhabitants of the archipelago would mi- 

 grate, and no closely consecutive record of their modifications 

 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 v/ould oftenest produce 

 new varieties; and the varieties would at first 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, and 

 as they would be found embedded in slightly different substages 

 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 formations, an 

 infinite number of those fine transitional forms which, on our 

 theory, 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, 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 formation, would, by many palaeontologists, 

 be ranked as distinct species. But I do not pretend that I should 

 ever have suspected how poor was the record in the best pre- 

 served geological sections, had not the absence of innumerable 



