422 SCIENCE PROGRESS 



sidence of the reef foundations would be established for barrier 

 reefs, and made more probable than any other theory for atolls 

 also. But, as if to add new interest to this old problem, two 

 other causes of submergence, independent of reef-foundation 

 subsidence, have been suggested : one is a general rise of ocean 

 level, due to uplift of some part of the ocean floor outside of 

 the coral-reef regions, the consequences of which have been 

 set forth chiefly by Vaughan 1 ; the other is the rise of ocean 

 level due to the melting of Pleistocene ice sheets, as outlined 

 some years ago by Belt, Upham, and Penck, and as recently 

 analysed in detail by Daly. 8 



Distinction between Subsidence and Submergence. — The solu- 

 tion of the coral-reef problem therefore depends at present 

 upon the discovery of some means of discriminating among 

 the three causes of submergence indicated above. No means 

 of absolute discrimination are known, because so many elements 

 of the problem are beyond the reach of observation ; but 

 various considerations lead me to regard changes of ocean level 

 as of secondary importance and to attribute the submergence 

 which is demanded by reef-encircled islands, and which is 

 therefore made probable for atolls as well, to local subsidence, 

 essentially as Darwin and Dana supposed. The reasons for 

 this opinion may be briefly stated. 



As to a general rise of ocean level caused by an uplift of 

 some part of the ocean floor, this cause of submergence is dis- 

 carded, not only because it demands extravagant measures of 

 ocean-floor uplift in order to produce the necessary changes 

 of ocean level, but also because the submergence that it would 

 produce must be everywhere of the same date, rate, and 

 amount ; whereas the features of various coral reefs demand 

 submergences varying in place, date, and amount, if not in 

 rate also. This aspect of the problem has been considered in 

 another article, 3 and need not be further pursued here. 



As to the sub-recent rise of ocean level caused bythe melting 

 of the Pleistocene ice sheets as a means of accounting for the 



1 T. W. Vaughan, " The Origin of Barrier Coral Reefs," Amer.Journ. Set. xli. 



1916, I3I-I35- 



1 R. A. Daly, " The Glacial-control Theory of Coral Reefs," Proc. Amer. Acad. 

 Arts and Set. li. 191 5, 157-251. 



* "A Shaler Memorial Study of Coral Reefs," Amer.Journ. Sci. xl. 191 5, 

 223-271 ; see p. 259. 



