522 W. M. DAVIS SUBSIDENCE OF REEE-ENCIRCLED ISLANDS 



of 40 fathoms at the change, already discussed, from a moderate slope to 

 a steep pitch on the exterior profile of barrier and atoll reefs, much better 

 explained as an aggradational adjustment of the platform margin to the 

 present action of waves and currents than as recording a surface of abra- 

 sion that was cut when the ocean was 30 or 40 fathoms lower than now. 

 The abundant and elaborately charted facts on which these statements 

 concerning the Philippines are based merit detailed treatment, for which 

 space can not be afforded here. 



It may, however, be the case that those who are convinced of the cor- 

 rectness of the Glacial-control theory would insist that platforms and 

 cliffs were really cut during the Glacial period on all the exposed coasts 

 of the Philippines, and that they are not to be detected today because 

 they have been greatly submerged or emerged since they were abraded; 

 but if so great a measure of postglacial deformation is accepted for the 

 Philippines, it is unreasonable to assume a long period of stability for the 

 Macclesfield, Tizard, and other banks in the China Sea which the Philip- 

 pines inclose from the Pacific; yet the processes of the Glacial-control 

 theory involve a period of stability for the bottom of that sea long enough 

 for the production of extensive banks by the degradation of volcanic 

 islands, almost as large as Hawaii, to low relief chiefly by subaerial ero- 

 sion in preglacial time, for their complete abrasion to submarine banks 

 by the waves of the lowered ocean during the Glacial period, and for the 

 more or less complete upgrowth of barrier reefs on the bank margins in 

 postglacial time. 



So long enduring a stability in a deep-sea basin bordering a continental 

 margin of the Pacific Ocean seems to me not only inherently improbable 

 on general principles, but seriously discredited by the many signs of 

 geologically modern movements in the Philippines and elsewhere in the 

 Australasian archipelagoes, whether such movements have caused the dis- 

 appearance of abraded platforms and cliffs or not. The assumption of 

 prolonged stability of the islands or banks thereabouts is, indeed, without 

 sound support; no warrant for the assumption, based on an inquiry into 

 the geological history of neighboring islands and continental coasts, has 

 been published, and, as far as I can learn, no such warrant can be found. 

 The explanation of the banks in the China Sea by the processes of the 

 Glacial-control theory — among which two processes, the killing of the 

 reefs and the abrasion of platforms, are already discredited by the absence 

 of spur-end cliffs on the central islands of close-set barrier reefs in other 

 regions — thus becomes improbable in a very high degree. 



