or
that group to assort that the theory of oceanic permanence is quite
inconsistent with the distribution of its various species and genera.
Because a few Indian genera and closely allied species of birds are
found in Madagascar, a land termed "Lemuria" has been supposed to have
united the two countries during a comparatively recent geological epoch;
while the similarity of fossil plants and reptiles, from the Permian and
Miocene formations of India and South Africa, has been adduced as
further evidence of this connection. But there are also genera of
snakes, of insects, and of plants, common to Madagascar and South
America only, which have been held to necessitate a direct land
connection between these countries. These views evidently refute
themselves, because any such land connections must have led to a far
greater similarity in the productions of the several countries than
actually exists, and would besides render altogether inexplicable the
absence of all the chief types of African and Indian mammalia from
Madagascar, and its marvellous individuality in every department of the
organic world.[169]

_Powers of Dispersal as illustrated by Insular Organisms._

Having arrived at the conclusion that our existing oceans have remained
practically unaltered throughout the Tertiary and Secondary periods of
geology, and that the distribution of the mammalia is such as might
have been brought about by their known powers of dispersal, and by such
changes of land and sea as have probably or certainly occurred, we are,
of course, restricted to similar causes to explain the much wider and
sometimes more eccentric distribution of other classes of animals and of
plants. In doing so, we have to rely partly on direct evidence of
dispersal, afforded by the land organisms that have been observed far
out at sea, or which have taken refuge on ships, as well as by the
periodical visitants to remote islands; but very largely on indirect
evidence, afforded by the frequent presence of certain groups on remote
oceanic islands, which some ancestral forms must, therefore, have
reached by transmission across the ocean from distant lands.

_Birds._

These vary much in their powers of flight, and their capability of
traversing wide seas and oceans. Many swimming and wading birds can
continue long on the wing, fly swiftly, and have, besides, the power of
resting safely on the surface of the water. These would hardly be
limited by any width