IMPERFECTION OF GEOLOGICAL RECORD 271 



On the sudden appearance of whole groups of Allied 

 Species. — The abrupt manner in which whole groups 01 

 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 allowance for the enormous intervals of time, 

 which have probably elapsed between our consecutive 

 formations, — longer perhaps in most cases than the 

 time required for the accumulation of each formation. 

 These intervals will have given time for the multipli- 

 cation of species from some one or some few parent- 

 forms ; and in the succeeding formation such species 

 will appear as if suddenly created. 



1 may here recall a remark formerly made, namely 

 that it might require a long succession of ages to adapt 

 an organism to some new and peculiar line of life, for 

 instance to fly through the air ; but that when this had 

 been effected, and a few species had thus acquired a 

 great advantage over other organisms, a comparatively 

 short time would be necessary to produce many divergent 



