384 



ISLAND LIFE. 



[part it. 



and may leave the ancient fauna in a very fragmentary state ; 

 while subsequent elevations may have brought it so near to the 

 continent that some immigration even of mammalia may have 

 taken place. If these elevations and subsidences occurred several 

 times over, though never to such an extent as again to unite the 

 island with the continent, it is evident that a very complex 

 result might be produced ; for besides the relics of the ancient 

 fauna, we might have successive immigrations from surrounding 

 lands reaching down to the era of existing species. Bearing in 

 mind these possible changes, we shall generally be able to arrive 

 at a fair conjectural solution of the phenomena of distribution 

 presented by these ancient islands. 



Undoubtedly the most interesting of such islands, and that 

 which exhibits their chief peculiarities in the greatest perfec- 

 tion, is Madagascar, and we shall therefore enter somewhat fully 

 into its biological and physical history. 



Physical features of Madagascar. — This great island is situated 

 about 250 miles from the east coast of Africa, and extends 

 from 12° to 25^ S. Lat. It is almost exactly 1,000 miles 

 long, with an extreme width of 860 and an average width of 

 more than 260 miles. A lofty granitic plateau, from eighty to 

 160 miles wide and from 3,000 to 5,000 feet high, occupies its 

 central portion, on which rise peaks and domes of basalt and 

 granite to a height of nearly 9,000 feet; and there are also 

 numerous extinct volcanic cones and craters. All round the 

 island, but especially developed on the south and west, are 

 plains of a few hundred feet elevation, formed of rocks which 

 are shown by their fossils to be of Jurassic age, or at all events 

 to belong to somewhere near the middle portion of the Secondary 

 period. The higher granitic plateau consists of bare undulating 

 moors, while the lower Secondary plains are more or less wooded ; 

 and there is here also a continuous belt of dense forest, varying 

 from six or eight to fifty miles wide, encircling the whole island, 

 usually at about thirty miles distance from the coast but in the 

 north-east coming down to the sea-shore. 



The sea around Madagascar, when the shallow bank on which it 

 stands is passed, is generally deep. This 100-fathom bank is only 

 from one to three miles wide on the east side, but on the west 



