CHAPTER XI 



THE PROGRESSIVE DEVELOPMEITT OF THE LIFE-WORLD^ AS 

 SHOWN BY THE GEOLOGICAL RECORD 



In order to form any adequate conception of the world of 

 life as a whole, of the agencies concerned in its development, 

 and of its relation to man as its final outcome, we must en- 

 deavour to learn something of its past history; and this can 

 only be obtained by means of the fossilised remains preserved 

 in the successive strata or layers of the earth's crust, briefly 

 termed " the geological record." In the preceding chapter I 

 have endeavoured to indicate the forces that have been at work 

 in continually moulding and remoulding the earth's surface; 

 and have argued that the frequent changes of the physical en- 

 vironment thus produced have been the initial causes of the 

 corresponding changes in the forms of organic life, owing to 

 the need of adaptation to the permanently changed conditions; 

 and also to the opening up of new places in the economy of 

 nature, to be successively filled through that divergency of 

 evolution which Darwin so strongly insisted upon as a neces- 

 sary result of variation and the struggle for existence. 



But in order to appreciate the extent of the changes of the 

 earth's surface during the successive periods of life-develop- 

 ment, it is necessary to learn how vast, how strange, and yet 

 how gradual were those changes ; how they consisted of alter- 

 nate periods of not only elevation and depression, but also of 

 alternations of movement and of quiescence, the latter often 

 continuing for long periods, during which more and more 

 complete adaptation was effected, and, perhaps in consequence 

 a diminished preservation in the rocks, of the life of the period. 

 Thus have occurred those numerous " breaks " in the geo- 

 logical record which separate the great " eras " and " sys- 



203 



