208 |W. M. DAVIS 
further considered later. Perhaps the corals were very generally 
killed, but the nullipores were not; if so, the nullipores, although 
unable to construct a reef alone, might cover and protect the exposed 
flanks of an already constructed reef for a geologically brief epoch 
until the corals could again establish themselves upon it. 
The floors of atoll lagoons—Whatever solution the question of 
the survival of reef-building corals during the glacial period may 
eventually receive, it may be set aside for the present and return 
may be made to the main facts upon which the glacial-control 
theory is built, with the question, Is it really impossible to explain 
the smoothness of atoll-lagoon floors and of submarine banks with- 
out prolonged abrasion of still-standing islands? This seems to 
me no impossibility. Those smooth surfaces are not the result 
of abrasion, even if an abraded surface exists beneath them; they 
are the result of the even distribution of organic sediments by 
agencies now in operation, whatever the shape of the foundation 
that the sediments rest upon, as will appear from the following 
consideration. 
As to atolls, it is true that the waters of their lagoons are 
generally placid, but it is also true that at times of storm they are 
agitated sufficiently to become turbid by stirring up the bottom 
sediments. Gardiner’s testimony on this point, based on observa- 
tions in the Maldives, is important: 
~ It is only in a few protected situations, where the depth is as great as 
40 fathoms or more, that the lagoon bottom appears not to be churned up by 
the currents and waves. In heavy weather the lagoon water is almost milky, 
and floating surface nets [for zodlogical collecting ?] are almost useless on 
account of the enormous amount of mud in suspension. The total amount 
of mud that passes out of the lagoon in the water is enormous.? 
Hence I cannot accept Daly’s statements that ‘‘the lagoon floor 
. is little or not at all disturbed by any waves or currents 
generated in the lagoon itself,” and that ‘‘the filling and smoothing 
out of the hypothetical ‘moat’’’ about a subsiding island is little 
aided by the mud from the reef. “The coarser detritus’? washed 
in from the reef flat often does “‘form a well-defined terrace slowly 
tJ. S. Gardiner, “‘The Origin of Coral Reefs... . ,” Amer. Jour. Sct., XVI 
(1903), 203-13; see p. 2I0. 
