302 IMPERFECTION OF THE Chap. IX. 



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

 tend 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 commence- 

 ment 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 palaeontologists, for instance, by 

 Agassiz, Pictet, and by none more forcibly than by 

 Professor 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 into life all at once, the fact would be fatal to 

 the theory of descent with slow modification through 

 natural selection. For the development of a group 

 of forms, all of which have descended from some 

 one progenitor, must have been an extremely slow 

 process ; and the progenitors must have lived long ages 

 before their modified descendants. But we continually 

 over-rate the perfection of the geological record, and 

 falsely infer, because certain genera or families have 

 not been found beneath a certain stage, that they did 

 not exist before that stage. We continually forget 

 how large the world is, compared with the area over 

 which our geological formations have been carefully 

 examined ; we forget that groups of species may else- 

 where have long existed and have slowly multiplied 

 before they invaded the ancient archipelagoes of Europe 

 and of the United States. We do not make due allow- 

 ance for the enormous intervals of time, which have 



