CHAP. X.] GEOLOGICAL RECORD. 249 



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 Jife tend to supplant the old and un- 

 improved 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 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 as- 

 suredly, if this theory be true, such have lived upon the earth. 



On, tlie 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 Ly ell's grand work on the Principles of Geology, which 

 the future historian will recognise as having produced a revolu- 

 tion 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 surface of the land has been denuded, and 

 how much sediment has been deposited. As Lyell has well re- 

 marked, 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 examino 

 for himself the great piles of superimposed strata, and watch the 

 rivulets bringing down mud, and the waves wearing away the sea- 

 cliffs, in order to comprehend something about the duration of 

 past time, the monuments of which we see all around us. 



It is good to wander along the coast, when formed of moderately 

 hard rocks, and mark the process of degradation. The tides in 

 most cases reach the cliffs only for a short time twice a day, and 

 the waves eat into them only when they are charged with sand ot 



