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Show B8G ISLAND LH'l1~. [t·An1' tr. ---------- it is much broader and stretches out opposite Mozambique to a distance of about eighty miles. The Mozambique Channel varies from less than 500 to more than 1,500 fathoms deep, the shallowest part being where the Com oro Islands and adjacent shoals seem to form stepping-stones to the continent of Afric...,a. The 500-fathom line includes Aldabra and the small ] arquhar Islands to the north of Madagascar; while to the cast the sen deepens rapidly to the 1,000-fathom line, and then more slowly, a profound channel of 2,400 fathoms separating Madagascar from Bourbon and Mauritius. To the north-east of Mauritius are a. series of extensive shoals, forming four large banks less than 100 fathoms below the surface, while the 1,000-fathom line includes them all, with an area about half that of Madagascar itself. A little further north is the Seychelles group, also standing on an extensive 1,000-fat.hom bank, while aU· around the sea is more than 2,000 fathoms deep. It seems probable, then, that to the north-east of Madagascar there was once a series of very large islands, separated from it by not very wide straits; while eastward across the Imli:~.n Ocean we find the Chagos and J\'l.aldive coral atolls, markin_s the position of other large islands, which together would form a line of communication, by comparatively easy stages of 4-00 or 500 miles each between Madagascar and India. These submerged islands, as shown in our map at p. 386, are of great importance in explaining some anomalous features in the zoology of this great island. If the rocks of Secondary age which form a belt around the island are held to indicate that Madagascar was once of loss extent than it is now (though this by no means necessarily follows), we have also evidence that it has recently been considerably larger ; for along the east coast there is an extensive barrier coral-reef about 350 miles in length, and varying in distance from the land from a quarter of a mile to three or four miles. This is good proof of recent subsidence; while we have no record of raised coral rocks inland which would certainly mark any recent elevation, because fringing coral reefs surround a considerable portion of the northern, eastern, and south·· western coasts. We may therefore conclude that during CHAP. XIX.] TIIE MADAGASCAR GROUP. 387 |