CORAL REEFS AND SUBMARINE BANKS 200 
explanation by the subsidence theory evidently demands precisely 
the “ordinary course of events’ postulated by Darwin, namely, 
subsidence after a long interval of rest. But let it be at once added 
that the glacial-control theory here supplements Darwin’s theory 
in an effective manner by calling attention to the glacial oscillations 
of ocean-level, for a lowering of the ocean surface combined with 
a subsidence of reef foundations will produce the equivalent of a 
“stationary period,” and a later rise of ocean-level combined with 
continued subsidence will cause an unusually rapid submergence; 
thus the apparent discontinuity of origin between a submerged 
atoll plain and the narrow young reefs that surmount it finds an 
explanation that is especially applicable to postglacial time. This 
aspect of the problem is referred to again below. 
Ii sudden submergence, such as that which separated the 
formation of reefs A and B’, take place after the formation of atoll E, 
its upgrowth will not be continued; it then becomes a drowned 
atoll, of which Chagos bank in the Southern Indian Ocean, and the 
Macclesfield bank in the China Sea, may be examples. But it 
is singular that no banks of this kind are known with a greater 
depth than 60 or 70 fathoms; this aspect of the problem is especially 
considered in later sections. 
_In all the reefs shown in section in Fig. 1, three different struc- 
tures are to be distinguished: first, the reef proper, composed in 
part of coral and other shallow-water organisms in place, as well 
as of disorderly masses of coral and much fine detritus; second, 
the exterior talus, pitching steeply to deep water and composed of 
coarse and fine detritus obliquely stratified, including a mixture of 
down-washed shallow-water organisms with others that lived at 
greater depths; and third, the interior lagoon deposits, horizontally 
stratified and composed chiefly of inwashed organic detritus from 
the reef, of outwashed inorganic detritus from the island, in 
decreasing quantity upward, and of locally supplied organic 
deposits; but the lagoon deposits may also include corals in place, 
representing reef patches and pillars in the lagoon as well as belts of 
fringing reef along the inner margin. 
The reef proper, composed, at least in part, of corals in place, is, 
as Darwin saw (118), a comparatively small fraction of the total 
