208 THE LAPSE OF TIME. Chap. IX, 



forms might have ilescended from the other; lor 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, while 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 varieties of the 

 same species at the present day ; and these parent-species, 

 now generally extinct, have in their turn been similarly con- 

 nected with more ancient species ; and so on backward, always 

 converging to the common ancestor of each great class. So 

 that the number of intermediate and transitional links, be- 

 tween all living and extinct species, must have been incon- 

 ceivably great. But assuredly, if this theory be true, such 

 have lived upon the earth. 



On the Lapse of Time, as inferred from the Mate of Deposi- 

 tion and Extent of Denudation. 



Ind(^pendently of our not hnding 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 etlected very sIomIv. It is 

 hardh' possible for me even to recall to the reader, who is not 

 a practical geologist, the facts leading the mind feebly to com- 

 prehend the lapse of time. He who can read Sir Cliarles 

 Ly ell's grand Avork on the Principles of Geology, which the 

 future historian will recognize as having produced a revolu- 

 tion in natural science, 3'et does not admit how vast have been 

 the past periods of time, may at once close this volume. Not 

 that it suffices to study the Princij^les of Geology, or to read 

 special treatises by d liferent observers on separate formations, 

 and to mark how each author attempts to give an inadequate 

 idea of the duration of each formation or even of each stratum. 

 We can best gain some idea of jiast time by knowing the agen- 

 cies at work, and learning how nuich of the surface of the land 

 has l)cen denuded, and how nnich sediment has been deposited. 

 As I.yell has well remarked, the extent and thickness of our 



