308 W. M. DAVIS 
effects of “clouds of sediments’’ (211), as Daly suggests, this cause 
of failure being evidently as applicable to a drowned atoll as to an 
abraded platform, is a good subject for future investigation. 
It is not only in general, but also in certain details that the 
theory of subsidence applies to the reefs of the Indian Ocean. 
Gardiner notes that “‘a most important point of difference in the 
Maldives from north to south lies in the gradual increase of the 
banks [lagoon floors] in depth,” but as recent subsidence is to him an 
“‘absolute impossibility’ he finds no satisfactory explanation for the 
increase. The large-scale Admiralty charts of the Maldives show 
the northern lagoons to be from 20 to 25 fathoms deep, and the 
southern ones from 4o to 45 fathoms, the change being accomplished 
in about 4oo nautical miles. Darwin knew these facts and said in 
the first edition of his book, ‘‘I can assign no adequate cause for this 
difference in depth” (’42, 34), but he added in the second edition, 
“excepting that the southern part of the Archipelago has subsided 
to a greater degree or at a quicker rate than the northern part”’ 
(74, 47). No one has since then offered any better explanation. 
It may be added that the Great Chagos bank lies about 300 miles 
south of the Maldives, and therefore Darwin’s interpretation of it 
as a drowned atoll falls in very well with his explanation of the 
southward deepening of the Maldive lagoons. When one recalls 
the various lines of geological evidence that point to the change of a 
large land area to a deep-sea bottom in the western part of the 
Indian Ocean, it seems as unreasonable to exclude recent sub- 
sidence from this region as to exclude it from the center of the 
China Sea. 
Control of depth of submarine banks.—It is not only the flatness 
of submarine banks that has been regarded as beyond explanation 
by the subsidence theory; the accordance of their depths with 
respect to present sea-level has also been instanced as impossible 
of explanation by any other cause than prolonged abrasion of still- 
standing islands by the lowered glacial ocean. As to their origin 
by abrasion, suffice it to repeat the argument already stated, 
namely, if preglacial islands of almost any composition as broad 
as the larger submarine banks were completely truncated by the 
waves of the lowered glacial ocean, then the spur ends of maturely 
