562 AV. M. DAVIS SrBSIDEXCE OF EEEF-EXCIRCLED ISLANDS 



account for the reefs of the unstable western Pacific in some other wa}^ 

 But in Daly's exposition of the theory the tables of depths for reefs and 

 banks, by averages from which the theory is thought to be strongly sup- 

 ported, include examples from Fiji, Xew Caledonia, Queensland, the 

 Solomon Islands, and the China Sea, as if the reefs of these regions had 

 developed under the same conditions of long enduring stability as those 

 of the mid-Pacific. The Macclesfield bank, in the last-named area, is in 

 particular mentioned on several pages as if, in spite of excessive depth of 

 49 fathoms in the central part of its aggraded floor, and notwithstanding 

 its nearness to the greatly disturbed region of the Australasian archi- 

 pelagoes, it still supported a theory in which long enduring stability is an 

 essential j^ostulate and in which the lowering of the abrading ocean, 

 though liberally estimated, is placed between 2" and 33 fathoms; for al- 

 though uplift or subsidence is not regarded as impossible in the areas 

 studied, it is said to be ^'necessarily slight.'" The reasons already adduced 

 for regarding the China Sea as a region of instability appear to me suffi- 

 cient to invalidate the explanation of the Macclesfield banks and its neigh- 

 bors by the Glacial-control theory. 



In view of the abundant evidence of instability in the region of the 

 Australasian archipelagoes, including that furnished by the unconfor- 

 mable fringing reefs of the Philippines, as above stated, and in view of the 

 reasonable explanation for decrease of lagoon depth with decrease of atoll 

 diameter that is furnished by the subsidence theory as well as by the Gla- 

 cial-control theory, and again in view of the large departures of individual 

 depth values from average values, precisely as the subsidence theory, but 

 not the Glacial-control theory, would lead us to exj)ect, I am constrained 

 to believe that the statistical argument advanced by Daly for the stability 

 of reef foundations, based on average depths of lagoon and banks, must 

 be misleading. Indeed, the argument may have to be turned the other 

 way round; for if the mean values of the individually discordant depths 

 of atoll lagoons and submarine banks in areas that are independently 

 proved to have suffered frequent and recent movements of upheaval and 

 subsidence, nevertheless accord with mean-depth values for atoll lagoons 

 in the mid-Pacific region, it must be concluded that mean depth values 

 are no safer indication of stability in the latter areas of unknown be- 

 havior than they are in the former areas of kno^\^i disturbance. 



The detailed Form of Islaxd Spur Exds as Evidexce for 

 ixtermittext subsidexce 



A section may here be given to certain minor features of many reef- 

 encircled island to which attention has seldom if ever been called, al- 



