CORAL REEFS AND SUBMARINE BANKS 409 
drowned by a rapid submergence which the postglacial rise of ocean- 
level may have helped to produce. 
Darwin's theory of the Pacific Ocean.—After Darwin had con- 
ceived the theory of subsidence and found that it accounted for the 
few reefs that he had himself seen as well as for many reefs seen by 
other explorers, he made further test of it by inquiring whether 
it would account for the distribution of reefs, and wrote on this 
aspect of the problem in his Journal of Researches on the ‘‘ Beagle”’ 
(1840, pp. 566, 567) as follows: 
When we consider the absence of both widely encircling [barrier] reefs and 
lagoon islands [atolls] in the several archipelagoes and wide areas, where there 
are proofs of elevation [in the form of ‘‘raised shells and corals, together with 
mere skirting (fringing) reefs’’]; and on the other hand the converse case of the 
absence of such proof where reefs of those classes do occur; together with the 
juxtaposition of the different kinds produced by movements of the same 
order, and the symmetry of the whole, I think it will be difficult (even inde- 
pendently of the explanation it offers of the peculiar configuration of each 
class) to deny a great probability of this theory. 
That candid statement contains the essence of a simple means 
of verification and serves to contradict those who later complained 
that Darwin had assumed that subsidence proved itself. He em- 
ployed the same means of verification twenty years later in the 
Origin of Species, regarding which he wrote, “‘I believe in the doc- 
trine of descent with modification, notwithstanding that this or 
that particular change of structure cannot be accounted for, because 
this doctrine groups together and explains . . . . many general 
phenomena of nature.”” Unfortunately the two additional means 
of verification for the theory of intermittent subsidence as provided 
by embayed shore lines and unconformable contacts were not used 
by its author, but that aspect of the problem need not be further 
considered here.» 
The occurrence of fringes, barriers, and atolls was more fully 
discussed in Darwin’s book on The Structure and Distribution of 
Coral Reefs (1842); here an appendix of 50 pages presents a sum- 
mary of all records then available, the results of which were shown 
upon a map; and it was these results that led to certain generaliza- 
tions as to broad areas of subsidence and of elevation in the Pacific 
which later observations have not confirmed. Darwin did not “ven- 
ture to hope that the map is free from many errors,” as he had to 
seek ‘“‘information from all kinds of sources,” but he trusted that 
