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Show 384 ISLAND LIFE. (l'Afi'l' 1[, 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 immi<Yration even of mammalia may have 0 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 eviden,t that a very complex result might be produced; for besides the relics of the ancient fauna., we might have successive immigro.tions from snrrounding lands reaching down to the era of existing species. Bearing in mind these possibJe changes, we shall generally be ab!e to arrive at a fair conjectural solution of the phenomena of distribution presented by these ancient islands. Undoubtedly the most interesting of such islands, aml that which exhibits their chief peculia.rities in the greatest perfection, is Madagascar, and we shall therefore enter so mew hat 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-r S. Lat. It is almost exactly 1,000 miles long, with an extreme width of 360 and an average wioth of more than 2GO 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 isla.nd, 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 undulatin<Y moors, while the lower Secondary plains are more or less wooded~ and there is here also a continuous belt of dense forest varyin<Y ' 0 from six or eight to fifty miles wide, encircling the whole island, usual1y 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 CHAP. XIX.) THE MADAGASCAR GROUP. 385 1teunion. ~It |