440 SCIENCE PROGRESS 



in the same ocean that, although both must have been formed 

 after the submergence by which the valleys of the two islands 

 were embayed, it seems impossible that both should have been 

 formed in the same period of time ; Rodriguez must have been 

 submerged before Mane ; hence the submergence preceding the 

 formation of the Rodriguez reef and the submergence preceding 

 the formation of the Mane reefs do not appear to have been caused 

 by a single, uniform, and universal rise of ocean level. Con- 

 versely, the 8o-ft. emergence of the elevated reef on Mahe, the 

 1,200-ft. emergence of Christmas Island in the eastern Indian 

 Ocean, and the absence of all signs of emergence on many 

 reef-encircled volcanic islands of the Pacific, cannot be explained 

 by a fall of ocean level everywhere of the same amount. Like- 

 wise, the elevated but undissected Loyalty atolls, at altitudes 

 of 200 or 300 ft., and the elevated reefs in Fiji at various 

 altitudes up "to 1,030 ft., partly or largely dissected, cannot be 

 explained by a fall of ocean level, everywhere of the same 

 amount and date. 



All the difficulties that thus embarrass the theories which 

 regard reef-encircled islands and reef-bordered continental coasts 

 as stationary, while the ocean rises or falls around them, vanish 

 if the islands and coasts which serve as foundations for reef 

 growth are supposed to be subject to such movements as are 

 postulated in Darwin's theory ; that is, to slow or intermittent 

 movements of elevation and of subsidence, which vary in place, 

 amount, rate, and date, and which are frequently or generally 

 greater in measure and more rapid in rate than fluctuations of 

 ocean level ; not that no such fluctuations occur, but that the 

 many indications of submergences and emergences, varying 

 in place, date, and amount, demand local movements of the 

 submerged or emerged land or island, and not universal and 

 equable changes of ocean level for their explanation. The 

 chief value of such universal changes of level, especially of those 

 caused by the climatic variations of the Glacial period, lies in 

 their modification of the amount of submergence or emergence 

 due to local movements of subsidence or elevation. This 

 aspect of the problem has been elsewhere discussed. 1 



Darwin's Theory of Intermittent Subsidence. — If reef founda- 

 tions are regarded as unstable, lateral reef growth will take 



1 " Problems Associated with the Study of Coral Reefs," Scietit. Motithly, li. 

 1916; see p. 565. 



