sea in early Tertiary times, forming
a large island-continent. By the evidence of abundant organic remains we
know that all the types of large mammalia now found in Africa (but which
are absent from Madagascar) inhabited Europe and Asia, and many of them
also North America, in the Miocene period. At a still earlier epoch Africa
may have received its lower types of mammals--lemurs, insectivora, and
small carnivora, together with its ancestral struthious birds, and its
reptiles and insects of American or Australian affinity; and at this period
it was joined to Madagascar. Before the later continental period of Africa,
Madagascar had become an island; and thus, when the large mammalia from the
northern continent overran Africa, they were prevented from reaching
Madagascar, which thenceforth was enabled to develop its singular forms of
low-type mammalia, its gigantic ostrich-like Aepyornis, its isolated birds,
its remarkable insects, and its rich and peculiar flora. From it the
adjacent islands received such organisms as could cross the sea; while they
transmitted to Madagascar some of the Indian birds and insects which had
reached them.

The method we have followed in these investigations is to accept the
results of geological and palaeontological science, and the ascertained
facts as to the powers of dispersal of the various animal groups; to take
full account of the laws of evolution as affecting distribution, {449} and
of the various ocean depths as implying recent or remote union of islands
with their adjacent continents; and the result is, that wherever we possess
a sufficient knowledge of these various classes of evidence, we find it
possible to give a connected and intelligible explanation of all the most
striking peculiarities of the organic world. In Madagascar we have
undoubtedly one of the most difficult of these problems; but we have, I
think, fairly met and conquered most of its difficulties. The complexity of
the organic relations of this island is due, partly to its having derived
its animal forms from two distinct sources--from one continent through a
direct land-connection, and from another by means of intervening islands
now submerged; but, mainly to the fact of its having been separated from a
continent which is now, zoologically, in a very different condition from
that which prevailed at the time of the separation; and to its having been
thus able to preserve a number of types which may date back to the E