IMPERFECTION OF GEOLOGICAL RECORD 57 



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 con- 

 verging 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 Depo- 

 sition 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 historian 

 will recognize as having 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 



