CHAt. X.J GEOLOalOAL RECORD. 49 



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 occurring everywhere throughout nature, depends 

 on the very process of natural selection, through which 

 new varieties continually take the places of and sup- 

 plant 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 formation and every stra- 

 tum full of such intermediate links? Geology assured- 

 ly does not reveal any such finely-graduated organic 

 chain; and this, perhaps, is the most obvious and seri- 

 ous objection which can be urged against the theory. 

 The explanation lies, as I believe, in the extreme imper- 

 fection 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 difiicult, when 

 looking at any two species, to avoid picturing to my- 

 self 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 gen- 

 erally have differed in some respects from all its modi- 

 fied descendants. 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- 



