IMPERFECTION OF GEOLOGICAL RECORD 55 



the forms which they connect, will generally be beaten 

 out and exterminated during the course of further modi- 

 fication 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 

 just in 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 for- 

 mation and every stratum full of such intermediate links? 

 Geology assuredly does not reveal any such finely- 

 graduated organic chain; and this, perhaps, is the most 

 obvious and serious objection which can be urged against 

 the theory. The explanation lies, as I believe, in the 

 extreme imperfection of the geological record. 



In the first place, it should always be borne in mind 

 what sort of intermediate forms must, on the theory, 

 have formerly existed. I have found it difficult, whea 

 looking at any two species, to avoid picturing to myself 

 forms directly intermediate between them. But this is a 

 wholly false view; we should always look for forms 

 intermediate between each species and a common but 

 unknown progenitor; and the progenitor will generally 

 have differed in some respects from all its modified de- 

 scendants. To give a simple illustration: the fantail and 

 pouter pigeons are both descended from the rock-pigeon; 

 if we possessed all the intermediate varieties which have 

 ever existed, we should have an extremely close series 

 between both and the rock-pigeon; but we should have 

 no varieties directly intermediate between the fantail and 



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