408 W. M. DAVIS 
the Pacific; nor that the argument based on the dissimilarity of 
central depths in intertropical and extra-tropical banks is necessarily 
fatal to the origin of the intertropical banks by the abrasion of still- 
standing preglacial islands. But, on the other hand, it does seem 
fair to urge that the abrasion of intertropical and extra-tropical 
banks can hardly have taken place (if it took place at all) at the 
same level, because of the present differences in their central depths; 
that the stability of the submarine banks in the China Sea, as 
postulated by the glacial-control theory, is made at least improbable 
by the instability of the neighboring islands and sea floors; and 
- that, if the stability of these typical banks is improbable, then the 
stability of all the other banks and of atolls as well is rendered 
very uncertain; for if one smooth bank can be produced on an 
unstable foundation without the aid of abrasion, then the occurrence 
of smooth banks elsewhere and of smooth atoll-lagoon floors is no. 
proof of stability. 
Furthermore, it seems reasonable to question the value of the 
often-recurring depth of 4o fathoms at the margin of submarine 
banks and around coral-reef slopes as an indication of a former 
1 owered level of the ocean, and to inquire, as above, whether it may 
not be an adjustment of aggraded surfaces to the present level of the 
ocean. In view of these various uncertainties on the one hand 
and open possibilities on the other, it is not an inherent strength, 
but an easily avoided weakness, of the glacial-control theory, espe- 
cially when it is applied to such banks as those of the China Sea 
and hence presumably when applied to atolls in general, to main- 
tain that no important vertical movements of the earth’s crust are 
included in the processes by which atolls are produced. We may, 
indeed, in view of the reasons given on page 390 for discrediting 
the abrasion of atolls and low volcanic islands during the glacial 
period, and in view of the reasons later adduced against the long- 
continued stability in the China Sea, make special application of the 
results of this inquiry by saying that the Macclesfield bank cannot 
be safely regarded as representing a volcanic island, once as large 
as Hawaii, that has stood still long enough to be worn down to low 
relief and that was then planed off by the glacial ocean; it much 
more probably represents a large atoll, formed by upgrowth during 
the long-continued, slow subsidence of its foundation, and recently 
