CORAL REEFS AND SUBMARINE BANKS 401 
processes and of waves and currents. The history of adjacent 
islands indicates, as has already been shown, that long-enduring 
stability is not a necessary condition of the ocean floor in general, 
and that it is by no means a probable condition of the parts of the 
ocean floor where certain submarine banks occur. As to the 
accumulation of organic deposits on submarine banks, that is mani- 
fest enough; but the mere occurrence of such deposits does not 
prove that the banks are standing still instead of rising or sinking, 
or that loose deposits can aggrade a bank to small depths in the 
open ocean where heavy swell frequently sweeps over it. The 
submarine banks described by Buchanan’ and Murray? may or 
may not exemplify the Rein-Murray theory of atolls; they cer- 
tainly do not demonstrate its correctness. 
In view of the slow accumulation and continual disintegration 
of organic sediments and of the increasing action of waves and 
currents upon them as their depth decreases, it is possible that the 
depth of submarine banks may be in some instances controlled 
through a rough balance between degradation by waves and cur- 
rents as well as deepening by slow subsidence and aggradation 
by accumulating sediment. Whatever their origin, the accumula- 
tion of organic detritus will tend to build up the surface; and here 
be it noted that although aggradation by inwash of detritus from a 
drowned reef rim is less effective in large banks than in small ones, 
aggradation by precipitation of floating organisms and by accumu- 
lation of bottom organisms is not affected by area; for the larger 
the area the more numerous the organisms; a very large bank may 
therefore be built up about as fast as one of medium size. On coral 
reefs there are numerous agencies, from gnawing fish and grinding 
sea slugs to boring worms and adhering algae, which reduce coral 
rock to sand and silt of such fineness that it can be easily shifted by 
the waves and currents of the lagoons. If similar disintegrating 
1T. Y. Buchanan, ‘‘On Oceanic Shoals Discovered by the SS. ‘Dacia’... . ,” 
Proc. Roy. Soc. Edinb., XIII (1886), 428-43. These banks and several others off the 
coast of Africa Beewacs the Canary Islands and Spain are shown on Hydrogr. Office 
chart 1743; they are all less than 10 miles in diameter; their depths vary from 23 to 
96 fathoms. 
2 J. Murray, ‘‘Balfour Shoal, a Submarine Elevation in the Coral Sea,” Scot. 
Geogr. Mag., XIII (1897), 120-34. 
