Even in this case, how
small would the chance be of a seed falling on favourable soil, and
coming to maturity! But it would be a great error to argue that
because a well-stocked island, like Great Britain, has not, as far as
is known (and it would be very difficult to prove this), received
within the last few centuries, through occasional means of transport,
immigrants from Europe or any other continent, that a poorly-stocked
island, though standing more remote from the mainland, would not
receive colonists by similar means. I do not doubt that out of twenty
seeds or animals transported to an island, even if far less
well-stocked than Britain, scarcely more than one would be so well
fitted to its new home, as to become naturalised. But this, as it
seems to me, is no valid argument against what would be effected by
occasional means of transport, during the long lapse of geological
time, whilst an island was being upheaved and formed, and before it
had become fully stocked with inhabitants. On almost bare land, with
few or no destructive insects or birds living there, nearly every
seed, which chanced to arrive, would be sure to germinate and survive.
DISPERSAL DURING THE GLACIAL PERIOD.
The identity of many plants and animals, on mountain-summits,
separated from each other by hundreds of miles of lowlands, where the
Alpine species could not possibly exist, is one of the most striking
cases known of the same species living at distant points, without the
apparent possibility of their having migrated from one to the other.
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