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 re¬ 
gions 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 ar¬ 
ranged in the same order, in accordance with the gene¬ 
ral succession 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 
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 liv¬ 
ing 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 
