CORAL REEFS AND SUBMARINE BANKS 201 
or so-called ‘drowned atolls” of the coral seas are next reviewed, 
first as to the necessity of abrasion instead of aggradation for 
their production and secondly as to the probability of their having 
stood still, as preglacial volcanic islands, long enough to be worn 
down and more or less abraded instead of having suffered intermit- 
tent subsidence. Both of these questions are answered in favor of 
Darwin’s theory; thus these banks give less evidence for the 
glacial-control theory than has been claimed for them. Extra- 
tropical banks, where abrasion is attested by the clift shores of 
the residual islands, are then compared with the banks of the 
coral seas, where abrasion is hypothetical: it thus appears probable 
that the lowering of the ocean during the glacial period was much 
less than 4o fathoms. 
The general result of the ee is that the long-enduring 
stability of reef foundations and the abrasion of reefs and islands 
by the chilled and lowered ocean of the glacial period are, to say the 
least, extremely improbable; and therefore that coral reefs are 
better explained by subsidence and aggradation than by stability 
and abrasion; and further that subsidence of considerable amounts 
has probably combined with changes of ocean-level of small amounts 
in determining the conditions under which the sea-level reefs of 
today have been formed. 
Intermittent subsidence as postulated in Darwin’s theory.—The 
degree of opposition between the two theories here to be discussed 
may be learned by citing a number of pertinent passages from the 
original expositions by their authors. Darwin found warrant for 
the postulate of subsidence in his geological researches, which gave 
“every reason for believing that there are now large areas gradually 
sinking, in the same manner as others are rising. . . . . When we 
consider how many parts of the surface of the globe have been 
elevated within recent geological epochs, we must admit that there 
have been subsidences on a corresponding scale, for otherwise the 
whole globe would have swollen (Structure and Origin of Coral 
Reefs, 1842, p. 95). Since the voyage of the ‘‘Beagle” a larger 
knowledge of the earth’s history has been gained, as a result of 
t Additional citations from Darwin’s Structure and Origin of Coral Reefs will be 
given by page numbers only. 
