386 W. M. DAVIS 
becomes complicated. The dimensions of some of the largest 
banks in nautical miles and fathoms are as follows: 
Bank Location Length Breadth Central Depth 
IMViaieclestiel dts ae reeere China Sea 95 35 55-60 
ized eects as care pf aS 25 IO 48 
Se@eyCaalles soocecengc000s Indian Ocean 200 80 40 
Great Chagos=) asses. a of go 70 48 
ANIMUNMIS 5 soc one anced i e 90 20 30 
INamaulkalpesenieei ner Pacific Ocean 30 25 45 
The Macclesfield bank, the largest of several submarine banks 
in the China Sea, is a good example. Interesting accounts of it 
have been published by the British Admiralty.‘ It possesses an 
incomplete rim, occupied by living corals, which rises around the 
margin to minimum depths of about 1o fathoms. Nowif this bank 
has an abraded platform for a foundation, the depth of the platform: 
should increase from the center outward and should be at least 
ro or 15 fathoms more at the margin than at thecenter. Hence the 
bank margin, originally 55 or 60 fathoms and now only 10 fathoms 
below present sea-level, must have been built up at least 45 or 50 
fathoms in postglacial time, and at half-distance from margin to 
center the bank must have been aggraded 15 or 20 fathoms in order 
to convert its initial flat cone into the present shallow saucer. But 
if so much change has taken place outside of the center, the center 
itself must have been significantly aggraded, and its actual depth 
is therefore not a true measure of the depth of its buried rock 
foundation. 
The same uncertainty prevails as to the depth, not to say the 
very existence, of the supposed rock platforms that are assumed 
to serve as foundations for other submarine banks. The Great 
Chagos bank of the Southern Indian Ocean, taken by Darwin as 
the type of a drowned atoll, measures go by 70 miles; it has a 
broad, flat floor, 48 fathoms in depth near the center, and a broad 
rim at an average depth of 16 fathoms, from which a narrower 
rim rises nearer to the surface. The Amirante bank, in the same 
tW. U. Moore and P. W. Bassett-Smith, China Sea... . Tizard, and Maccles- 
field Banks, Hydrog. Dept., Admiralty, London, 1889. P. W. Bassett-Smith, Dredg- 
ings Obtained on the Macclesfield Bank, Ibid., 1894. 
