57 
affinities of the flora and fauna of different places accord with 
the mode of origination thus assumed. 
First, then of the means of dispersal. To enter into this 
at all at length would require the whole evening ; it must suf- 
fice, therefore, to allude to a couple of instances of a very dif- 
ferent hut equally important character, by way of illustration. 
The close affinity between the Arctic flora on high mountains 
in all parts of the world, however remote, appears a case 
of peculiar difficulty. How can the supposed common pro- 
genitors of these nearly allied or even identical species, so 
different from those existing in the adjoining temperate or 
tropical countries, have become distributed into their several 
places ? The answer is found in the prevalence at a compara- 
tively recent period of great cold over large portions of the 
earth/s surface, accompanied with glaciers and other Arctic 
phenomena. Such increased cold would naturally drive the 
Arctic flora of the north pole southwards in all directions over 
districts now utterly uncongenial to it. On the diminution of 
the cold, this flora would plainly retire not only northwards, 
but also up the mountains in all parts, the congenial portions 
of which, now so completely isolated, would thus be clothed 
everywhere with species drawn from a common source, exactly 
as we should surmise to have been the case from their intimate 
systematic relations. This instance is one where great appa- 
rent difficulty is turned into confirmation. The second is one 
which on the face of it remarkably confirms the hypothesis of 
common descent. Oceanic islands, if not peopled by special 
creation, can only conceivably have been peopled by birds, 
insects, seeds, &c., having been either blown or washed thither. 
Only some species, plainly, could thus be conveyed — e.g. of 
land mammals, only those which could fly, namely bats. It is 
a remarkable fact that the only mammals that are found on 
such islands ( i.e . those very far removed from the mainland) 
are precisely bats, just as this theory of distribution would 
require. But further, these bats are in many cases of peculiar 
species, found nowhere but in their several islands, exactly as 
might have been expected if they were the descendants of iso- 
lated individuals long ago blown thither. That they should 
be thus peculiar, and the only mammals found there, though 
others are fully as capable of living there, are facts alike in- 
explicable on the theory of special creations. 
But, secondly, of the relation between geographical connec- 
tion and the affinities of flora and fauna. This appears in many 
ways. Thus the species existing in different islands of a group, 
though often very distinct, are always more nearly related 
to one another than to those on the mainland. The flora and 
