6o THE PHYSICAL KINSHIP 



just the kind of life that lived in each age, but, by 

 comparing the species of successive strata, can 

 construct with astonishing fulness the genealogi- 

 cal outline of the entire life process. The suc- 

 cession of life forms as they appear in the rocks, 

 with a sketch of their probable genealogy, is traced 

 elsewhere in this chapter. It is only necessary to 

 say here that the order in which the forms of life 

 appear in the sedimentary strata is that of a 

 gradually increasing complexity. The inverte- 

 brates appear first ; then the fishes, the lowest of 

 the vertebrates ; after these come the amphibians ; 

 following these the reptiles ; and finally the birds 

 and mammals. 



8. There is another reason for a belief in evolu- 

 tion furnished by geology, but of a somewhat 

 different kind from that just stated. It consists 

 in the fact that there are found in the rocks series 

 or grades of structures, which fit with amazing 

 accuracy on to the structures of existing species. 

 Now, this is precise^ what, according to the 

 evolutional hypothesis, is to be expected. For, if 

 evolution is true, existing species represent the 

 tops of things. They are the existing and visible 

 parts of processes vvhich extend indefinitely back 

 into the past, and whose deceased stages may 

 reasonably be expected to be found fossil in the 

 earth. Considering the youth and inexperience 

 of paleontology and the torn and incoherent 

 character of the record, it is surprising that anat- 

 omists have been able to accomplish what they 

 have accomplished. In many cases — notably, 



