Chap. X. AFFINITIES OF EXTINCT SPECIES. 329 



periods, — a formation in one region often corresponding 

 with a blank interval in the other, — and if in both 

 regions the species have gone on slowly changing 

 daring the accumulation of the several formations and 

 during the long intervals of time between them ; in 

 this- case, the several formations in the two regions 

 could be arranged in the same order, in accordance 

 with the general succession of the form of life, and the 

 order would falsely appear to be strictly parallel ; never- 

 theless the species would not all be the same in the 

 apparently corresponding stages in the two regions. 



On the Affinities of extinct Species to each other, and to 

 living forms. — Let us now look to the mutual affinities 

 of extinct and living species. They all fall into one 

 grand natural system ; and this fact is at once explained 

 on the principle of descent. The more ancient any 

 form is, the more, as a general rule, it differs from living 

 forms. But, as Buckland long ago remarked, all fossils 

 can be classed either in still existing groups, or between 

 them. That the extinct forms of life help to fill up the 

 wide intervals between existing genera, families, and 

 orders, cannot be disputed. For if we confine our atten- 

 tion either to the living or to the extinct alone, the 

 series is far less perfect than if we combine both into 

 one general system. With respect to the Vertebrata, 

 whole pages could be filled with striking illustrations 

 from our great palaeontologist, Owen, showing how ex- 

 tinct animals fall in between existing groups. Cuvier 

 ranked the Ruminants and Pachyderms, as the two most 

 distinct orders of mammals ; but Owen has discovered 

 so many fossil links, that he has had to alter the whole 

 classification of these two orders ; and has placed certain 

 pachyderms in the same sub-order with ruminants : for 

 example, he dissolves by fine gradations the apparently 



