28 MEETING OF THE BRITISH ASSOCIATION. 
oceanic migration, and applying to it the theory of variation and 
natural selection. 
The lecturer then pointed out the difficulties in the way of accepting 
this hypothesis of trans-oceanic migration, as accounting for all the 
insular floras, of which the chief are,— that these floras are not of a 
character intermediate between those of the continents between which 
the islets are placed, or scarcely at all so, but are characteristic of one 
continent only ; that the Azores have scarcely a single American plant ; 
that Kerguelen's Land has the flora of the continent most distant from 
it, and this no less than 4000 miles off; that it is extremely difficult 
to account by trans-oceanic migration, without intermediate' land, for 
the peculiar non-European plants of Madeira being common to itself 
and the Canaries and Azores; that to aid the transport of plants from 
continents to islands, Mr. Darwin does assume probable former inter- 
mediate islands, and, if islands be thus granted, why not continents ; 
that such large islands as are near continents and contain land mam- 
mals have, in Mr. Darwin's opinion, been peopled by previous conti- 
nental extension; and that it is difficult to draw an arbitrary line 
between large contiguous and more distant smaller islets ; that islands, 
as a rule, diminish in size with their distance from continents ; that 
there are large areas in the Malayan archipelago exposed to great oscil- 
lations of level, which, if partially submerged, would leave only the 
tops of their volcanic mountains exposed, greatly resembling oceanic 
islets; that in such a case as that, of Madeira, the Canaries, and 
Azores, it should follow that the more distant the island from the con- 
tinent the more peculiar the species, which is hardly the case; la ly, 
that in many cases the most prevalent continental species are not 
fonnd to be transported to any distance, as is the case in New Zealand, 
which does contain certain Australian plants, but not one of the 
genera of Acacia or Eucalyptus, though these form the staple of the 
Australian forests, and when introduced by man into New Zealand in- 
crease rapidly, to the extinction of the native vegetation. • 
On the whole, however, the lecturer was disposed to abandon the 
theory of continental extension, both because it had no solid basis and 
because it proved too much, accounting, as it were, for everything, and 
explaining nothing; and to accept the hypothesis of trans-oivanic 
migration, both because of its bring an undoubted vera cax.sa to a 
great extent, and because, as Mr. Darwin had shown, it did, with the 
