CORAL REEFS AND SUBMARINE BANKS 299 
growing inward from the reef,” as may be seen in many lagoons, 
for example, those of Tahiti and Raiatea in the Society Islands. 
Furthermore, as a large quantity of muddy sediment is formed on 
the reef flat by disintegrating agencies, organic and inorganic, 
acting on the blocks and scraps of coral rock washed in from the 
exterior reef face, and as the interior terrace of white granular 
detritus is free from fine silt, it follows that an important share of 
fine detritus from the reef must reach the lagoon floor; and this 
reef silt, as well as the fine organic sediments formed on the lagoon 
floor or in the lagoon waters, is distributed by the waves and 
currents therein generated, as Gardiner states. 
Darwin had earlier reached a fair understanding of this problem: 
“The greater part of the bottom in most lagoons is formed of sedi- 
ments; large spaces have exactly the same depth, or the depth 
varies so insensibly that it is evident that no other means, excepting 
aqueous deposition, could have levelled the surface so equally” 
(26). In my own limited experience I saw the waters of two 
barrier-reef lagoons rolling in heavy waves under strong winds— 
once in Fiji, once in the broad lagoon of the Great Barrier reef off 
the Queensland coast—and on both occasions the water was gray 
with suspended sediments. It seems evident that under such 
conditions the finer sediments of lagoon floors will be lifted chiefly 
from the shallower parts and will settle in about the same amount 
everywhere; and the continuation of such changes will tend to 
produce and maintain a fairly smooth surface of sedimentation, 
such as actually exists. 
Another view has been announced. After assigning a small 
value to the general distribution of lagoon sediments by the waves 
of gales and storms, and a large value to the distribution of sedi- 
ments by currents driven under steady winds, Daly has recently 
reached the conclusion that lagoon floors thus aggraded during 
subsidence should not be level, but should be deeper to windward 
and shallower to leeward; then, on examining charts of atolls and 
verifying the general levelness of lagoon floors, he concludes that 
subsidence has not taken place, but that the reefs have grown up 
and the lagoons have been evenly aggraded in postglacial time 
because their sediments have been deposited on smoothly abraded 
