390 W. M. DAVIS 
their supposed abraded platforms, which according to the glacial- 
control theory should be some 20 fathoms deeper; and in adding 
that Wharton “rightly regarded this flatness as fatal to the Darwin- 
Dana theory” (196), he disregards the capacity of lagoon waves 
in true atolls and of the ocean swell over submerged atolls or banks 
to produce smooth lagoon floors, whatever the form of the buried 
foundation. This capacity seems to me well proved. Hence, as 
far as the features of atolls and submarine banks are concerned, the 
necessity of accepting the glacial-control theory is not constraining; 
the possibility of accounting for the form and the depths of atoll- 
lagoon floors and of submarine banks as a result of their slow, 
variable, intermittent subsidence is still open. 
Supposed abraded platforms beneath submarine banks.—The 
variations In the depths of atoll-lagoon floors and of submarine 
banks, although of considerable measure, are, with the exception 
of the Saya de Malha bank, by no means so great as to be altogether 
incompatible with the existence of abraded platforms at uniform 
depths beneath them, as required by the glacial-control theory; 
but they seem to me too great to demonstrate the correctness 
of that theory to the exclusion of all others. On the contrary, 
they throw a certain amount of doubt upon the theory by the 
necessity that they impose of making a number of unproved, 
perhaps unprovable, assumptions in order to bring about a sufh- 
cient agreement among various unlike quantities. This doubt 
may be solved arithmetically by saying: “‘Since probably not more 
than 5 to 25 m. can be allowed for the thickness of the post- 
glacial calcareous veneer in the wider lagoons, the accordance of 
platform depths for the wider lagoons and reefless banks seems 
Cleaners The agreement is visible in spite of possible, though 
necessarily slight, uplift or subsidence”’ (Daly, 193, 194); but sucha 
solution is not convincing. It involves the venturesome postulate 
of a long-enduring still-stand of the islands concerned, the very 
questionable process of abrasion while the reefs were supposedly 
dead, and the entirely unknown total thickness of calcareous 
deposits in lagoons and on banks. A solution containing so many 
undetermined quantities must remain very uncertain. The uncer- 
tainty will be more apparent if we return to the case of the 
