oVZ 



IMPERFECTION OF THE 



CHAPTER X. 



Cl^ THE IMPERFECTIOI^^ OF THE GEOLOGICAL RECORD. 



On tlie absence of intermediate varieties at the present day— On the 

 nature of extinct intermediate varieties; on their number — On 

 the lapse of time, as inferred from the rate of denudation and of 

 deposition— On the lapse of time as estimated by years — On the 

 poorness of our palaeontological collections — On the intermittence 

 of geological formations — ^On the denudation of granitic areas — 

 On the absence of intermediate varieties in any one formation — 

 On the sudden appearance of groups of species— On their sudden 

 appearance in the lowest known fossiliferous strata — Antiquity 

 of the habitable earth. 



In the sixth chapter I enumerated the chief objections 

 which might be justly urged against the views maintained 

 in this volume. Most of them have now been discussed. 

 One, namely, the distinctness of si^ecific forms and their 

 not being blended together by innumerable transitional 

 links, is a very obvious difficulty. I assigned reasons why 

 such links do not commonly occur at the present day under 

 the circumstances apparently most favorable for their pres- 

 ence, namely, on an extensive and continuous area with 

 graduated physical conditions. I endeavored to show, that 

 the life of each species depends in a more important manner 

 on the presence of other already defined organic forms, than 

 on climate, and, therefore, that the really governing condi- 

 tions of life do not graduate away quite insensibly like 

 heat or moisture. I endeavored, also, to shov/ that inter- 

 mediate varieties, from existing in lesser numbers than 

 the forms which they connect, will generally be beaten out 

 and exterminated during the course of further modifica- 

 tion and improvement. The main cause, however, of 

 innumerable intermediate links not now occurring every- 

 where throughout nature, depends on the very process of 

 natural selection, through which new varieties continually 

 take the places of and supplant their parent-forms. But 



