THE IMPERFECTION OF THE GEOLOGICAL RECORD 271 



form had remained for a very long period unaltered, while its de- 

 scendants had undergone a vast amount of change; and the prin- 

 ciple 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 differences 

 not greater than we see between the natural and domestic varie- 

 ties of the same species at the present day; and these parent spe- 

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

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

 converging to the common ancestor of each great class. So that 

 the number of intermediate and transitional links, between all 

 Hving 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 Ly ell's grand work on the Princi- 

 ples of Geology, which the future historian will recognize as hav- 

 ing produced a revolution in natural science, and yet 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 Principles of 

 Geology, or to read special treatises by different 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 past time by 

 knowing the agencies at work, and learning how deeply the sur- 

 face of the land has been denuded, and how much sediment has 

 been deposited. As Lyell has well remarked, the extent and 

 thickness of our sedimentary formations are the result and the 

 measure of the denudation which the earth's crust has elsewhere 

 undergone. Therefore a man should examine for himself the 

 great piles of superimposed strata, and watch the rivulets bring- 

 ing down mud, and the waves wearing away the sea-cliffs, in order 



