90 Revieics — Wallace s Idand Life. 



3. Ancient continental islands. — The extraordinaiy complexity of 

 the organic relations of Madagascar, says Mr. Wallace, is due, partly 

 to its having received its animal forms from two distinct sources, 

 but mainl}'^ to its having been separated from a continent now 

 zoologically in a different condition. The facts and reasonings of 

 this important chapter, though in the main zoological, have a distinct 

 geological bearing. Madagascar has not the characteristic animals 

 of either Africa or Asia. Half the existing species consist of Lemui's. 

 In fact, the island is a sort of Zoological Garden of high antiquity, 

 free from the ravages of the large Carnivora, where decajnng groups 

 of creatures, which have elsewhere perished or become scarce, 

 maintain a comparatively secluded existence. 



Why is this so ? When Madagascar Avas united to Africa, from 

 which it is at present separated by waters of considerable depth, the 

 adjacent continent was then entirely severed from Arctogsea by the 

 nummulitic sea, and constituted a sort of Australia, poor in the 

 higher forms of life. The upheaval of this sea-bed in Miocene times 

 admitted the higher types of mammalia, which were developed in 

 the great Euro-Asiatic continent, to the mainland of Africa, but 

 Madagascar had then become an island, and the great beasts were 

 thus excluded from it. We know from the rich deposits of fossil 

 mammals in the Miocene beds of Europe and N.W. India that the 

 great African mammals inhabited those regions. 



These reasonings tend to explain the absence of certain forms ; we 

 must next consider the origin of the existing groups. Doubtless 

 Madagascar, through the mainland of Africa, had an earlier union with 

 Arctog£ea, though it is rather a strong assumption that, otherwise, it 

 could never have obtained any mammalia (p. 391). However, the 

 Lemurs, Inseetivores, and Civets are known to have inhabited Europe 

 during the Eocene and Miocene periods, and thus a certain geo- 

 graphical link is established between the ends of groups now wide 

 asunder. The dispersal of these groups, superinduced by changes 

 of surface and climate, throughout long ages of geological time, may 

 thus serve to render possible an explanation of such an extreme case 

 as that of the insectivorous Centetidce, now confined to Madagascar 

 and the West Indies. 



The question whether the birds of Madagascar require the adop- 

 tion of the hypothetical Lemuria is scarcely one to be discussed in 

 the Geological Magazine. There are about one hundred and five 

 land birds, all but four or five being peculiar. When we consider 

 that the Azores, more than thrice as far from the mainland, contain 

 but one bird peculiar to them, and bear in mind also that the 

 author regards their whole avifauna as the result of recent immigra- 

 tion, voluntary or involuntary, we can only express surprise at the 

 unenterprising character of the birds of East Africa, who do not care 

 to cross the Mozambique channel, though the Comoro Islands offer a 

 series of convenient halting-places. 



The chapters on New Zealand, and on the Arctic element in South 

 Temperate Floras, complete the details of Island Life — a work which 

 is certain to be extensively read, and which is full of instructive 



