no known currents, whether of water or air, or ordinary means of transport
(20/3. Darwin's note on transportation (found with Forbes' letter):
"Forbes' arguments, from several Spanish plants in Ireland not being
transported, not sound, because sea-currents and air ditto and migration of
birds in SAME LINES. I have thought not-transportation the greatest
difficulty. Now we see how many seeds every plant and tree requires to be
regularly propagated in its own country, for we cannot think the great
number of seeds superfluous, and therefore how small is the chance of here
and there a solitary seedling being preserved in a well-stocked country."),
would account for the little group of Asturian plants--few as to species,
but playing a conspicuous part in the vegetation--giving a peculiar
botanical character to the south of Ireland; that, as I had produced
evidence of the other floras of our islands, i.e. the Germanic, the
Cretaceous, and the Devonian (these terms used topographically, not
geologically) having been acquired by migration over continuous land (the
glacial or alpine flora I except for the present--as ice-carriage might
have played a great part in its introduction)--I considered it most
probable, and maintained, that the introduction of that Irish flora was
also effected by the same means. I held also that the character of this
flora was more southern and more ancient than that of any of the others,
and that its fragmentary and limited state was probably due to the plants
composing it having (from their comparative hardiness--heaths, saxifrages,
etc.) survived the destroying influence of the glacial epoch.

My geological argument now is as follows: half the Mediterranean islands,
or more, are partly--in some cases (as Malta) wholly--composed of the
upheaved bed of the Miocene sea; so is a great part of the south of France
from Bordeaux to Montpellier; so is the west of Portugal; and we find the
corresponding beds with the same fossils (Pecten latissimus, etc.) in the
Azores. So general an upheaval seems to me to indicate the former