380 DARWINISM chap. 



whelming idea does this give us of the destruction of whole 

 piles of rock, miles in thickness and covering areas comparable 

 with those of continents ; and how great must have been the 

 loss of the innumerable fossil forms which those rocks con- 

 tained ! In view of such destruction we are forced to conclude 

 that our palaeontological collections, rich though they may- 

 appear, are really but small and random samples, giving no 

 adequate idea of the mighty series of organism which have 

 lived upon the earth. ^ 



Admitting, however, the extreme imperfection of the geo- 

 logical record as a whole, it may be urged that certain limited 

 portions of it are fairly complete — as, for example, the various 

 Miocene deposits of India, Europe, and North America, — 

 and that in these we ought to find many examples of species 

 and genera linked together by intermediate forms. It may be 

 replied that in several cases this really occui's ; and the reason 

 why it does not occur more often is, that the theory of 

 evolution requires that distinct genera should be linked 

 together, not by a direct passage, but by the descent of both 

 from a common ancestor, which may have lived in some much 

 earlier age the record of which is either wanting or very in- 

 complete. An illustration given by Mr. Darwin Avill make this 

 more clear to those who have not studied the subject. The 

 fantail and pouter pigeons are two very distinct and unlike 

 breeds, which we yet know to have been both derived from the 

 common Avild rock-pigeon. Now, if we had every variety of 

 living pigeon before us, or even all those which have lived 

 during the present centiu"y, we should find no intermediate 

 types between these two — none combining in any degree the 

 characters of the pouter with that of the fantail. Neither 

 should Ave ever find such an intermediate form, even had there 

 been preserved a specimen of every breed of pigeon since 

 the ancestral rock -pigeon was first tamed by man — a 

 period of probably several thousand years. We thus sec 

 that a complete passage from one very distinct species to 

 another could not be expected even had we a complete record 

 of the life of any one period. What we require is a complete 



1 The reader who desires to understand this subject more fully, should 

 study chap. x. of tlie Origin of Species, and chap. siv. of Sir Charles Lyell's 

 Principles of Geology. 



