560 AV. M. DAVIS SUBSIDENCE OF REEF-ENCIRCLED ISLANDS 



1916) of the first and last of the tliree. If these atolls were formed in 

 the neighborhood of so unstable an archipelago as the Solomons, it can 

 hardly be assumed that the atolls of the central Pacific need a long period 

 of nearly perfect stability for their production. The same argument may 

 be based on the atolls of the China Sea, in the neighborhood of the un- 

 stable Philippines. 



THE VOLUME OF REEFS 



The expectation of similarity in the cross-section dimensions of barrier 

 and atoll reefs that follows from the Glacial-control theory is not so well 

 confirmed by the facts as the opposite expectation that follows from the 

 subsidence theory. Some reefs, like those of Borabora, in the Society 

 group, are broad; others, like those of Budd reef, in northeastern Fiji, 

 are narrow; still others, like those which rim several banks north of Fiji, 

 do not reach sealevel, although their location provides as good opportu- 

 nity for upgrowth as is provided in Fiji for more successful reefs; and 

 some submerged banks have no reef rims, although their situation seems 

 as favorable for reef growth as that of neighboring rimmed banks. Great 

 variations in the breadth of fringing reefs, from almost zero to three 

 miles, may also be pointed out, but as this subject is more fully treated in 

 the forthcoming article in Journal of Geology (1918, a) it need not be 

 further pursued here. 



Allusion may be here made to the assumption included in the Glacial- 

 control theory that a truncated volcanic island, lying at a depth of about 

 30 or 40 fathoms, should serve as the foundation for sealevel atolls; but 

 a number of uplifted and deeply dissected limestone islands in eastern 

 Fiji, which appear to have been atolls origuially, give no indication of 

 possessing such platforms, as I have lately shown elsewhere (1917, a). 



CONTRASTS OF THE CENTRAL AND THE WESTERN PACIFIC 



Several writers have called attention to certain contrasts between the 

 central and the western areas of the Pacific. The central and truly oceanic 

 area gives few indications of recent upheaval in the way of elevated reefs, 

 and few indications of rapid subsidence in the way of drowned atolls, 

 although atolls at sealevel are abundant and barrier reefs are numerous. 

 The western area, largely occupied by archipelagoes, gives innumerable 

 indications of recent, rapid, and great upheavals and subsidences, in the 

 way of displaced and deformed marine, formations of various kinds, in- 

 cluding coral reefs now at altitudes and at depths of 2,000 feet or more. 

 High-standing coral reefs are well known on various islands of the archi- 



