GEOLOGICAL RECORD. 295 



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

 will have existed between them. But such a case would 

 imply that one form had remained for a very long period 

 unaltered, while its descendants had undergone a vast amount 

 of change ; and the principle of competition between organ- 

 ism 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 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 backward, 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 

 infinitely 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 histo- 

 rian will recognize as having produced a revolution in nat- 

 ural 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 inade- 

 quate idea of the duration of each formation, or even of each 

 stratum. We can best gain some idea of past time by know- 

 ing the agencies at work, and learning how deeply the surface 

 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 



