CORAL REEFS AND SUBMARINE BANKS 219 
platform remains as a more or less aggraded and nearly level 
submarine bank. 
The structures thus inferred are definite enough to establish the 
theory that accounts for them, if their existence be assured; but 
as only the form and the surface constituents of atolls and submarine 
banks are known, the theory which involves the undemonstrated 
existence of abraded platforms remains uncertain. The boring at 
Funafuti, the depth of which was about five times the difference 
of level assumed between S, and S,, Fig. 2, should have penetrated 
the detrital deposits, 7’’T’, below the reef proper, if that atoll were 
formed in the manner here stated; it might have penetrated vol- 
canic rocks also, as the section is here drawn, but no such rocks were 
reached. According to the theory of subsidence the boring might 
have penetrated true reef structure, or a combination of reef, 
lagoon, and talus structures, for its entire depth, as above noted. 
Some of the experts who have examined the rock core think that 
the boring was altogether in true reef-rock of shallow-water for- 
mation, some are noncommittal, some think it was mostly in talus 
deposits. Discrimination is doubtless difficult; but the evidence 
given by the absence of deep-water organisms from the boring is 
significant. A boring of similar depth in the lagoon center would 
have penetrated an abraded platform of volcanic rocks, if such a 
platform exists there; but several borings, all encountering volcanic 
rocks at the same moderate depth of about 40 fathoms, would be 
necessary to demonstrate that the rock surface had the form of a 
platform. 
The uniform postglacial rise of the ocean suggests that all 
existing reefs should be of similar volume above their abraded 
foundation; a later section is devoted to this point. The belief 
that the flatness of the floors of atoll lagoons and of submarine 
banks and the similarity of their depths can be explained only by 
their having almost flat platforms of uniform depth as foundations 
will also be examined later in some detail. Evidently, if atolls that 
had been formed according to the glacial-control theory were suffi- 
ciently elevated and dissected, the flat platform would be revealed 
if it existed; also this possibility is briefly considered in a later 
paragraph. 
