ARTICLES 429 



by the neglect of essential factors. Let it be here remembered 

 that the true interpretation of embayed shorelines was published 

 by Dana in 1 849, in an often-quoted report ; while the meaning 

 of unconformable contacts was recognised half a century earlier. 

 Surely the neglect of principles so well established in geological 

 science and so pertinent in discussions of coral reefs, vitiates 

 the conclusions that the discussions reach. 



The chief reason for this neglect seems to be that the origin 

 of coral reefs has been, as above noted, too often regarded as 

 a zoological problem, whereas it is in reality for the most part 

 a geological problem that can be solved only by geological 

 methods. A living reef is, to be sure, a superb aquarium, 

 where even a physiographer must marvel at the abundance, 

 the variety, and the beauty of the organic forms that flourish 

 upon it ; but the great body of the reef, from its inorganic 

 foundation up to the sea surface, is a huge rock mass, the 

 structural relations and the origin of which must be investigated 

 by the methods ordinarily employed by geologists in making 

 out the history of rock masses in general. A brief review of 

 the contributions made to the coral-reef problem by some of 

 its most noted investigators will show how far they have failed 

 to meet this requirement. 



Semper on the Reefs of the Pelew Islands. — Semper appears 

 to have had no experience as a geologist. His famous studies 

 of the Pelew Islands, which led him to the conclusion that the 

 reefs there seen were constructed during the elevation of their 

 foundations, must be rated as of little value when it is under- 

 stood that he assumed the islands to have been formed by 

 eruption below sea-level and to have emerged as a result of 

 uplift ; that he took no account of embayed shorelines or of 

 conformable or unconformable reef contacts ; and that he 

 rejected so manifest a possibility as a gentle tilting, by which 

 the southern part of the group, where elevated reefs occur, 

 would be raised, while the northern part, where atolls occur, 

 might be depressed. 1 



From all that Semper and other observers of the Pelew 



1 Semper's chief writings on this subject are : "Die EntstehungderCorallenriffe," 

 Verhandl. Phys.-med. Ges. Wiirzburg, i. 1869, vi-viii ; "Die Palau-Inseln im 

 Stillen Ozean," Leipzig, 1873 5 " Die natiirlichen Existenzbedingungen der Thiere," 

 Leipzig, 1880 ; translated as "Animal Life as Affected by Natural Conditions," 

 1881 ; see Chapters VII., VIII. 



