IMPEKFECT10N OJ? GEOLOGICAL RECORD. 293 



CHAPTER X. 



ON THE IMPERFECTION OF THE GEOLOGICAL RECOBD. 



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 Palaeontological Collections — On thelntermit- 

 tence 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 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 favorable for their presence, namely, on an 

 extensive and continuous area with graduated physical con- 

 ditions. 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 conditions of life do not graduate 

 away quite insensibly like heat or moisture. I endeavored, 

 also, to show that intermediate varieties, from existing in 

 lesser numbers than the forms which they connect, will gen- 

 erally be beaten out and exterminated during the course of 

 further modification and improvement. The main cause, 

 however, of innumerable intermediate links not now occur- 

 ring 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 in proportion as this process of extermina- 

 tion 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 



