290 W. M. DAVIS 
must therefore rest on nearly level rock platforms at a moderate 
and fairly uniform depth in all the coral seas. It is next argued 
that the production of the inferred rock platforms was preceded by 
subaérial erosion and marine abrasion during a long preglacial 
period of “‘general crustal stability in the coral sea,”’ whereby lofty 
volcanic islands were worn down to insular lowlands. Then, in 
view of the plausible inference that reef-making corals were killed 
during the glacial period, it is further supposed, as previously 
outlined, that the chilled and lowered ocean was free to cut away 
the dead reefs and to reduce the worn-down islands to flat platforms. 
Finally, as the ocean rose and warmed in postglacial time, the 
existing reefs are believed to have grown up around the platform 
margins, while unconsolidated calcareous deposits were strewn 
evenly over the platform surface; or, if reefs did not grow up, the 
platforms remained as submarine banks. 
The ingenuity with which the successive conditions and pro- 
cesses are enchained is certainly admirable, but the fundamental 
assumptions do not seem to be fully established, and the conclusions 
reached are not unescapable. The links of the chain of argument 
must be separately examined. The plausible inference that reef- 
making corals were killed during the glacial period will be con- 
sidered in the next two sections. 
Coral reefs not destroyed during the glacial period. ee is certainly 
plausible to suppose that reef-building corals may have been killed 
by the lowering of oceanic temperatures during the glacial epochs 
of the glacial period, but no sufficient tests of the correctness of 
this supposition have been brought forward. As far as I have been 
able to analyze the question, the reefs were not so completely 
divested of protecting organisms, except along the margin of the 
coral zone, as to expose them and their inclosed islands to abrasion, 
for the consequences of such abrasion are not found in the expectable 
form of spur-end cliffs (KN, Fig. 3b) on the central islands of 
fringing or of close-set barrier reefs, as I have elsewhere pointed out ;* 
hence this essential element of the glacial-control theory lacks 
1“ A Shaler Memorial Study of Coral Reefs,” Amer. Jour. Sci., XL (1015), 223-71; 
see pp. 236-46. ‘‘Problems Associated with the Study of Coral Reefs,” Sci. Monthly, 
II (1916), 559-77. 
