CORAL REEFS AND SUBMARINE BANKS 389 
fathoms) banks; the smaller banks are usually 25 fathoms deep, 
but the smallest are about as deep as the middle-sized banks: thus 
Turpie bank, 23 miles long, is 27 fathoms deep; for Alexa bank the 
figures are 18 and 24; Waterwitch, 105 and 25; Penguin, 9 and 
25; Hazel Holme, 5 and 25. The Saya de Malha bank in the 
Southern Indian Ocean southeast of the Seychelles bank is most 
exceptional in this respect; although only about 20 miles in diam- 
eter it has a central depth of 64 fathoms, with a rim of 20 fathoms 
or less around the northeastern margin. I have not been able to 
conceive of any way to account for this bank under the postulates 
of the glacial-control theory. 
As to banks of moderate size and of 20 or 25 fathoms depth, any 
platform that lies beneath them should be as deep as, indeed some- 
what deeper than, the platforms of the great banks; hence the 
thickness of the deposits by which the smaller banks are aggraded 
must measure at least 20 or 30 fathoms; but as this measure is 
obtained only by assuming that the platform exists at a proper 
depth, it has no particular value. 
It is interesting to note in passing that the central areas of the 
smaller reef-rimmed banks have extraordinarily smooth floors, 
presumably the work of the heavy swell that must sweep across 
their submerged rims and distribute very evenly all available 
sediments. It was, indeed, the smooth floors of these banks that 
led Wharton to abandon Darwin’s theory of subsidence, which he 
conceived as requiring a ‘“‘deeply concave surface” in the floors 
of atolls, whether their rims be at sea-level or below; he suggested 
instead that the flat floors of atoll lagoons and of submarine banks 
represented former volcanic islands, smoothly truncated by the 
waves of the ocean at its present level,’ and he tacitly postulated 
that reef-building corals were not present until the work of abrasion 
was completed. Daly gives a more reasonable statement of the 
conditions under which abrasion could act, but in saying, ‘“‘ Whar- 
ton’s choice of the agency which produced the flatness of lagoon 
floors and of banks seems irresistible,’ he does not make sufficient 
distinction between the evenly aggraded, reef-rimmed floors of the 
smaller submarine banks at such depths as 20 and 25 fathoms, and 
™W. T. L. Wharton [Address], Rep. Brit. Assoc. Adv. Sci. (1894), pp. 699-710. 
