. Island life : or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates . xactly1,000 miles long, with an extreme width of 360 and anaverage width of more than 260 miles. A lofty graniticplateau, from eighty to 160 miles wide and from 3,000 to5,000 feet high, occupies its central portion, on which risepeaks and domes of basalt and granite to a height ofnearly 9,000 feet; and there are also numerous extinctvolcanic cones and craters. All round the island, butespecially developed on the south and west, are plain
. Island life : or, the phenomena and causes of insular faunas and floras, including a revision and attempted solution of the problem of geological climates . xactly1,000 miles long, with an extreme width of 360 and anaverage width of more than 260 miles. A lofty graniticplateau, from eighty to 160 miles wide and from 3,000 to5,000 feet high, occupies its central portion, on which risepeaks and domes of basalt and granite to a height ofnearly 9,000 feet; and there are also numerous extinctvolcanic cones and craters. All round the island, butespecially developed on the south and west, are plains of afew hundred feet elevation, formed of rocks which areshown by their fossils to be of Jurassic age, or at all eventsto belong to somewhere near the middle portion of theSecondary period. The higher granitic plateau consists ofbare undulating moors, while the lower Secondary plainsare more or less wooded ; and there is here also a con-tinuous belt of dense forest, varying from six or eight tofifty miles wide, encircling the whole island, usually atabout thirty miles distance from the coast but in thenorth-east coming down to the sea-shore. ° E E 2. CHAP. XIX THE MADAGASCAR GROUP 414 The sea around Madagascar, when the shallow bank onwhich it stands is passed, is generally deep. This 100-fathom bank is only from one to three miles wide on theeast side, but on the west it is much broader, and stretchesout opposite Mozambique to a distance of about eightymiles. The Mozambique Channel is rather more than1,000 fathoms deep, but there is only a narrow belt of thisdepth opposite Mozambique, and one almost as narrowwhere the Comoro Islands seem to form stepping-stones to the continent of Africa. The 1,000-fathomline includes also Aldabra and the small FarquharIslands to the north of Madagascar ; while to the east thesea deepens rapidly to the 1,000-fathom line and thenmore slowly, a profound channel of 2,400 fathoms separat-ing Madagascar from Bourbon and Mauritius. To thenorth-ea
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