264 Imperfection of the Geological Record. Chap. x. 



CHAPTEE X. 



On the Imperfection of the Geological Eecord. 



On the 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 palseon- 



tological 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 dis- 

 tinctness of specific 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 favourable for 

 their presence, namely on an extensive and continuous area with 

 graduated physical conditions. I endeavoured 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 conditions of life do not 

 graduate away quite insensibly like heat or moisture. I endea- 

 voured, also, to show that intermediate varieties, from existing in 

 lesser numbers than the forms which they connect, will generally 

 be beaten out and exterminated during the course of further modifi- 

 ca ion and improvement. The main cause, however, of innumerable 

 intermediate links not now occurring everywhere 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 just m proportion as this process of extermination has 

 acted on an enormous scale, so must the number of intermediate 

 varieties, which have formerly existed, be truly enormous. Why 

 then is not every geological formation and every stratum full of 



