308 W. M. DAVIS 
the detritus to be transported and the agents of transportation with 
respect to present sea-level. Like the reef itself, the two elements 
of its exterior profile—namely, the gentler slope down to 40 fathoms 
and the steeper pitch below—have been brought by organic growth 
and by inorganic processes into a normal relation to sea-level. 
Secondly, regarding the free border of an uninclosed lagoon-floor 
sector of atolls and barrier reefs: In view of the alternate retarda- 
tion and acceleration of submergence. by the combination of 
prevalent subsidence with the periodic changes of ocean-level 
during the glacial period—for this is, in my mind, the chief value 
of the glacial-control theory—I am strongly inclined to regard any 
“platforms” that may exist, now more or less aggraded, beneath 
incompletely or completely inclosed lagoon floors as nothing more 
than the surface of earlier reefs normally broadened while sub- 
mergence was so slow that narrow reefs were transformed into 
mature reef plains. ‘Thus interpreted the present reefs are merely 
new, still young, and relatively narrow growths above their 
mature predecessors; narrow, because they have been developed 
while submergence has been accelerated. This inclination of 
opinion has been strengthened by an examination of charts of 
submarine banks both within and without the coral seas, and that 
aspect of the problem must next be examined. 
Let it be noted, however, that if the explanation above suggested 
for the change in the exterior slope of a reef at 40 fathoms depth 
be correct, then Daly’s conclusion that ‘‘the present atoll, barrier, 
and fringing reefs . . . . have been developed nearly or quite in 
the same interval of time” cannot be supported by the agreement 
of “their sectional areas and their volumes, as measured, in each 
case, above the break of slope at the platform on which the crown- 
ing reef stands” (233). A further conclusion is also vitiated, 
namely, that inasmuch as “the surface outcrops and volumes of the 
greater barrier and atoll reefs, measured from the levels of the 
lagoon floors, are respectively nearly equivalent in the Pacific and 
Indian oceans,” therefore “the earth’s crust must have sunk at 
a nearly uniform rate throughout the enormous area described 
. if these reefs were formed by subsidence” (233, 234). 
