258 W. M. Davis — Shaler Memorial Study of Coral Reefs. 



a rise of the sea surface, accompanied by a rise of those coasts 

 which do not show submergence and a still greater rise of 

 those that show emergence ; but although many coasts certainly 

 do show signs of recent submergence, many others do not ; and 

 even where recent submergence has taken place, its measm-e 

 and date are not known to be so closely alike as to demand a 

 rise of sea level for its explanation. Indeed, the explanation 

 of the submergence that is associated with the development of 

 barrier reefs by a general rise of sea level recalls Suess's explan- 

 ation of the recent emergence of certain high-standing coral 

 reefs by a general fall of sea level. Evidently, if all the high- 

 standing coral reefs were of the same height, as Suess some 

 thirty years ago thought they were, and if they were all simi- 

 larly undissected — a matter to which Suess gave no attention — 

 and if correspondingly recent and undissected shorelines were 

 found at the same altitude around most of the coasts of the 

 world, as Suess seems to have thought was the case, and if all 

 barrier-reef islands showed recent elevation instead of possess- 

 ing embayed shorelines — a matter which seems to have been 

 overlooked in Suess's argument — the accordant emergence of all 

 these features would be best explained by a fall of sea level : but 

 high-standing coral islands are now known to have very unlike 

 altitudes and to be very unequally dissected, while various conti- 

 nental and insular coasts indicate emergence and submergence 

 of the most diverse amounts and dates ; hence the phenomena of 

 emergence which Suess thought were simple and uniform and 

 widespread enough to be explained by a single fall of sea level, 

 are now found to be complex and diverse to such a degree that 

 they can be explained only by correspondingly complex and 

 diverse crustal movements, in addition to any universal change 

 of sea level that may have recently taken place. I cannot help 

 feeling that any appearance of a uniform measure of submerg- 

 ence in various barrier reefs and atolls will, when closely 

 studied, be found to include a significant measure of diversity; 

 and that whatever share of such submergence may be attrib- 

 uted to a universal rise of sea level, many local departures from 

 uniform submergence will remain to be explained by local 

 crustal movements. 



The fuller discussion of this aspect of the coral-reef problem 

 would require, first, a consideration of the large measures of 

 submergence at different dates that are involved in the forma- 

 tion of various coral reefs, some at sea level, some elevated ; 

 and second, a consideration of the terrestrial processes that are 

 involved in producing large measures of submergence at differ- 

 ent dates. As to the first consideration, let it suffice here to 

 point out that certain reefs of the Fiji group alone demand an 

 earlier submergence and others a later submergence, each of 



