THE LAPSE OF TIME 335 



other. Hence, in all such cases, we should be unable to rec- 

 ognise the parent-form of any two or more species, even if 

 we closely compared the structure of the parent with that of 

 its modified descendants, unless at the same time we had a 

 nearly perfect chain of the intermediate links. 



It is just possible by the theory, that one of two living 

 forms might have descended from the other; for instance, a 

 horse from a tapir; and in this case direct intermediate links 

 will have existed between them. But such a case would im- 

 ply that one form had remained for a very long period unal- 

 tered, whilst its descendants had undergone a vast amount 

 of change ; and the principle of competition between organism 

 and organism, between child and parent, will render this a 

 very rare event ; for in all cases the new and improved forms 

 of life tend to supplant the old and unimproved forms. 



By the theory of natural selection all living species have 

 been connected with the parent-species of each genus, by dif- 

 ferences not greater than we see between the natural and 

 domestic varieties of the same species at the present day ; and 

 these parent-species, now generally extinct, have in their 

 turn been similarly connected with more ancient forms ; and 

 so on backwards, always converging to the common ancestor 

 of each great class. So that the number of intermediate and 

 transitional links, between all living and extinct species, must 

 have been inconceivably great. But assuredly, if this theory 

 be true, such have lived upon the earth. 



ON THE LAPSE OF TIME, AS INFERRED FROM THE RATE OF 

 DEPOSITION AND EXTENT OF DENUDATION 



Independently of our not finding fossil remains of such in- 

 finitely numerous connecting links, it may be objected that 

 time cannot have sufficed for so great an amount of organic 

 change, all changes having been effected slowly. It is hardly 

 possible for me to recall to the reader who is not a practical 

 geologist, the facts leading the mind feebly to comprehend the 

 lapse of time. He who can read Sir Charles Lyell's grand 

 work on the Principles of Geology, which the future historian 

 will recognise as having produced a revolution in natural 

 science, and yet does not admit how vast have been the past 



