CHAP. XIX THE MADAGASCAR GROUP 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 com- 

 plexity 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-con- 

 nection, 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 Eocene, or even to the Cretaceous, period. Some of 

 these types have become altogether extinct elsewhere ; 

 others have spread far and wide over the globe, and have 

 survived only in a few remote countries — and especially in 

 those which have been more or less secured by their 

 isolated position from the incursions of the more highly- 

 developed forms of later times. This exj^lains why it is 

 that the nearest allies of the Madagascar fauna and flora 

 are now so often to be found in South America or 

 Australia — countries in which low forms of mammalia and 

 birds still largely prevail ; — it being on account of the 

 long-continued isolation of all these countries that similar 

 forms (descendants of ancient types) are preserved in them. 

 Had the numerous suggested continental extensions con- 

 necting these remote continents at various geological 

 periods been realities, the result would have been that all 

 these interesting archaic forms, all these defenceless insular 

 types, would long ago have been exterminated, and one 

 comparatively monotonous fauna have reigned over the 

 whole earth. So far from explaining the anomalous facts, 

 the alleged continental extensions, had they existed, would 

 have left no such facts to be explained. 



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