Appendix to Chapter V. 441 
the several ranges.’ Lastly, if instead of considering the 
case of alpine floras, we take the much larger case of the 
Old and New World as a whole, we meet with much larger 
proofs of the same general facts. For, “during the slowly 
decreasing warmth of the Pliocene period, as soon as the 
species in common, which inhabited the New and Old 
Worlds, migrated south of the Polar Circle, they will have 
been completely cut off from each other. This separation, 
as far as the more temperate productions are concerned, 
must have taken place long ages ago. As the plants and 
animals migrated southward, they will have become mingled 
in one great region with the native American productions, 
and would have had to compete with them; and, in the 
other great region, with those of the Old World. Conse- 
quently we have here everything favourable for much modifi- 
cation,—for far more modification than with the Alpine 
productions left isolated, within a much more recent period, 
on the several mountain ranges and on the arctic lands of 
Europe and N. America. Hence it has come, that when 
we.compare the now living productions of the temperate 
regions of the New and Old Worlds, we find very few iden- 
tical species; but we find in every class many forms, which 
some naturalists rank as geographical races, and others as 
distinct species; and a host of closely allied or representative 
forms which are ranked by all naturalists as specifically 
distinct.” 
In view then of all the above considerations—and 
especially those quoted from Darwin—it appears to me that 
far from raising any difficulty against the theory of evolution, 
the facts adduced by Mr. Carruthers make in favour of it. 
For when once these facts are taken in connection with the 
others above mentioned, they serve to complete the cor- 
fespondence between degrees of modification with degrees 
1 Origin of Species, p. 332. 
2 Tbid. pp. 333-4- 
