small group of the Galapagos Islands typifies,
and follows exactly the same laws in the distribution of its
inhabitants, as a great continent. How wonderful it is that two or three
closely similar but distinct species of a mocking-thrush{358} should
have been produced on three neighbouring and absolutely similar islands;
and that these three species of mocking-thrush should be closely related
to the other species inhabiting wholly different climates and different
districts of America, and only in America. No similar case so striking
as this of the Galapagos Archipelago has hitherto been observed; and
this difference of the productions in the different islands may perhaps
be partly explained by the depth of the sea between them (showing that
they could not have been united within recent geological periods), and
by the currents of the sea sweeping _straight_ between them,--and by
storms of wind being rare, through which means seeds and birds could be
blown, or drifted, from one island to another. There are however some
similar facts: it is said that the different, though neighbouring
islands of the East Indian Archipelago are inhabited by some different
species of the same genera; and at the Sandwich group some of the
islands have each their peculiar species of the same genera of plants.

{358} In the _Origin_, Ed. i. p. 390, a strong point is made of
birds which immigrated "with facility and in a body" not having
been modified. Thus the author accounts for the small percentage of
peculiar "marine birds."

Islands standing quite isolated within the intra-tropical oceans have
generally very peculiar floras, related, though feebly (as in the case
of St Helena{359} where almost every species is distinct), with the
nearest continent: Tristan d'Acunha is feebly related, I believe, in its
plants, both to Africa and S. America, not by having species in common,
but by the genera to which they belong{360}. The floras of the numerous
scattered islands of the Pacific are related to each other and to all
the surrounding continents; but it has been said, that they have more of
an Indo-Asiatic than American character{361}. This is somewhat
remarkable, as America is nearer to all the Eastern islands, and lies in
the direction of the trade-wind and prevailing currents; on the other
hand, all the heaviest gales come from the Asiatic side. But even with
the aid of these gales, it is not obvious on the ordinary theory of