264 SUDDEN APPEARANCE OF [CHAP. X 



the average duration of the same specific forms ; and these con- 

 tingencies are indispensable for the preservation of all the transi- 

 tional 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 

 climatal 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 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 would 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 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 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 preserved geological sections, had not 

 the absence of innumerable transitional links between the species 

 which lived at the commencement and close of each formation, 

 pressed so hardly on my theory. 



On the sudden Appearance of whole Groups of allied Species. 



The abrupt manner in which whole groups of species suddenly 

 appear in certain formations, has been urged by several palaeonto- 

 logists for instance, by Agassiz, Pictet, and Sedgwick as a fatal 

 objection to the belief in the transmutation of species. If numerous 

 species, belonging to the same genera or families, have really started 



