200 W. M. DAVIS 
curiously enough that, of the very few persons in this country 
who are now actively interested in the coral-reef problem, the two— 
Professor Daly and myselfi—who are especially concerned in the 
present discussion are long-time friends, present-day colleagues, 
and next-door neighbors. We have the same object in view, 
although our judgments differ as to the weight to be attached to 
various factors of our problem. We believe that our common 
object will be best reached through the open exposition of the 
many considerations that guide our opinions; and I for my part 
should be well satisfied if the competent critics who have admired 
the ingenuity with which Daly has set forth the possibilities of the 
glacial-control theory and who have been impressed by the strength 
that it has gained through his earnest advocacy should find in the 
following pages a fair comparison of its possibilities with those of 
Darwin’s theory. 
Plan of discussion.—The plan of discussion is as follows: The | 
chief postulates of the two theories regarding subsidence and 
stability will first be examined in order to make clear the strong 
contrasts between them. The reef structures consequent upon 
the postulates and processes of the two theories will then be deduced 
in order to discover the nature of the evidence that each theory 
demands for its support. Brief consideration will be given to the 
possible destruction of coral reefs during the glacial period as 
assumed by the glacial-control theory, with special attention to the 
evidence from Hawaii, Tahiti, and Murea; the conclusion is thus 
reached that reefs as a rule survived the epochs of glacial cooling, 
and hence that preglacial reefs were not abraded by the glacial 
ocean. The flatness of atoll-lagoon floors and the similarity of 
their depths will next be examined in order to learn whether the 
explanation of these features demands the truncation of pre- 
glacial islands by the waves of the lowered glacial ocean or whether 
they may be accounted for by aggradation during intermittent 
subsidence; the bearings of the exterior profile and the volume of 
existing reefs on the same question will also be inquired into; all 
with the result of showing that stability of reef foundations is not 
essential in accounting for these features, because they can also 
be accounted for as a result of subsidence. The submarine banks 
