CHAP. XK THE MADAGASCAR GROUP 



414 



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 it is much broader, and stretches 

 out opposite Mozambique to a distance of about eighty 

 miles. The Mozambique Channel is rather more than 

 1,000 fathoms deep, but there is only a narrow belt of this 

 depth opposite Mozambique, and one almost as narrow 

 where the Comoro Islands seem to form stepping- 

 stones to the continent of Africa. The 1,000-fathom 

 line includes also Aldabra and the small Farquhar 

 Islands to the north of Madagascar ; while to the east the 

 sea deepens rapidly to the 1,000-fathom line and then 

 more slowly, a profound channel of 2,400 fathoms separat- 

 ing 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-fathom bank, while all round 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 east- 

 ward across the Indian Ocean we find the Chagos and 

 Maldive coral atolls, perhaps marking the position of other 

 large islands, which together would form a line of 

 communication, by comparatively easy stages of 400 or 

 500 miles each between Madagascar and India. These 

 submerged islands, as shown in our map at p. 425, 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 less 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 



