Page - 333 - in The Origin of Species

CHAPTERX On the Imperfection of the Geological Record 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 palseontological collections—On the in- termittence 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 main- tained in this vohime. Most of them have now been dis- cussed. One, namely the distinctness 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 pres- ence, namely on an extensive and continuous area with grad- uated 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 endeavoured, also, to show that intermediate va- rieties, from existing in lesser numbers than the forms which they connect, will generally be beaten out and exterminated during the course of further modification and improvement. The inain cause, however, of innumerable intermediate links " not now occurring everywhere throughout nature, depends on the very process of natural selection, through which new va- rieties continually take the places of and supplant their parent-forms. But just in proportion as this process of ex- 333