CORAL REEFS AND SUBMARINE BANKS 387 
ocean, north of Madagascar, measures 90 by 20 miles, with a central 
depth of 30 fathoms and a rim generally under fo or 20 fathoms of 
water, bearing living coral and emerging in 21 low coral islands. 
Even more extraordinary is the vast Seychelles bank, east of the 
Amirante bank, the largest example of its kind; as represented on 
Admiralty chart 721, it measures about 200 by 80 miles; its general 
depth varies from 25 to 35 fathoms, with a maximum of 4o fathoms 
not far from the central island, Mahé, and with a shoal margin 
on the northeast where several reefs and coral-sand islands reach 
the surface. Here, as in the Macclesfield bank, the marginal 
depth of an abraded platform should be significantly greater than 
its center, and the present central depth of the bank is no safe 
measure of the depth of a platform beneath it. The central island, 
Mahé, represented in more detail on Admiralty chart 1072, is singu- 
lar in being composed of non-volcanic, granitic rocks; it measures 
17 by 4 miles, and its highest summit rises 2,993 feet above sea- 
level; its shore line is not clift, but beautifully embayed, with the 
bayheads occupied by delta plains and the dividing spurs trailing 
away in declining points with no cliffs at their ends.‘ Discontinu- 
ous fringing reefs border the points. Several other smaller granitic 
islands rise not far away. 
~ Mahé has, moreover, not only a narrow fringing reef at present 
sea-level, but also at a height of 80 feet patches of an elevated 
fringing reef,? which must, like the sea-level fringe, lie unconform- 
ably on the granitic slopes of the island; the date of the elevated 
reef with respect to the date of origin of the great submarine bank 
has not been studied by any of the visitors to the island—Pelly, 
Wright, Coppinger, Keller, Chun, Gardiner—whose accounts I 
have read; but if the elevated reef be the older of the two, it ought 
to have been completely worn away while the great bank, whatever 
its origin, was forming; and if the reef be the younger of the two, 
then while it was forming the great bank must have had a maximum 
1 Good views of the Mahé shoreline are given by C. Keller, Die ostafrikanischen 
Inseln (Berlin, 1898), p. 160; C. Chun, Aus den Tiefen des Weltmeeres (Jena, 1900), 
p. 432; and J. S. Gardiner, ‘‘The Indian Ocean,” Geogr. Jour., XXVIII (1906), 313-32, 
454-65; see p. 457. 
2C. Keller, op. cit., p. 158; C. Chun, op. cit., p. 426. 
