GEOLOGICAL SUCCESSION 295 



the species. If the several formations in these regions 

 have not been deposited during the same exact 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 during 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 suc- 

 cession of the form of life, and the order would falsely 

 appear to be strictly parallel ; nevertheless the species 

 would not all be the same in the apparently corre- 

 sponding 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, fami- 

 lies, and orders, cannot be disputed. For if we confine 

 our attention 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 Verte- 

 brata, whole pages could be filled with striking illustra- 

 tions from our great palaeontologist, Owen, showing how 

 extinct 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 

 wide difference between the pig and the camel. In 

 regard to the Invertebrata, Barrande, and a higher 

 authority could not be named, asserts that he is every 



