CHAP. XIX.] 
THE MADAGASCAR GROUP. 
419 
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 thence- 
forth was enabled to develop its singular forms of low-type mam- 
malia, its gigantic ostrich-like iEpyornis, 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, 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 
what it was 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 Eocene, or even to the Cretaceous, period. 
Some of these types have become altogether extinct else- 
where ; others have spread far and wide over the globe, and 
have survived only in a few remote countries — and especially in 
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