142 Reports & Proceedings — Geological Society of London. 



4. February 20, 1918. — George William Lamplugh, F.R.S., President, 



in the Chair. 



The following communication was read : — 



" Tiie Geological Aspects of the Coral Reef Problem." By- 

 Professor William Morris Davis, For. Corr. G.S. 



The communication is a critical review of the various theories 

 that have been put forward up to the present time to explain the 

 origin of coral reefs, A voyage in the Pacific, made in the year 

 1914, enabled the author to collect new evidence bearing upon the 

 question, and to make observations that have influenced him in his 

 support of Darwin's theory. 



After laying stress upon the embay ment of shore-lines as a proof 

 of subsidence, the author expresses the opinion that all theories that 

 postulate a fixed relation between reef formation and ocean level are 

 disproved, and are probably inapplicable to the case of atolls. It 

 appears certain that reef upgrowth is intimately associated with 

 submergence wherever the matter can be tested. The solution of 

 the coral reef problem turns at present upon some means of dis- 

 criminating between a submergence caused by subsidence and a sub- 

 mergence caused either by a general rise of the ocean level due to 

 the uplift of the ocean floor beyond the coral reef region or to the 

 melting of the Pleistocene ice-sheets. Although no means of such 

 discrimination are known, the author presents reasons that lead him 

 to regard changes in ocean level as of secondary importance, and that 

 have caused him to attribute the submergence demanded by self- 

 encircled islands to local subsidence, in accordance with the views of 

 Darwin and Dana. He regards the theory that presupposes the 

 raising of the ocean level bv uplift as extravagant in its demands, 

 and he finds the theory of "Glacial Control" inadequate when 

 applied to barrier reefs and encircled islands. 



Stress is laid on the highly significant unconformable relationship 

 that exists between reef and lagoon limestones and their foundations 

 — a feature that presents the strongest testimony for subsidence. 

 In such a case the foundations must have suffered ei'osion for a con- 

 siderable period before they were submerged, in preparation for the 

 unconformable deposition of reef limestones upon them. From 

 a consideration of such unconformable relations it is concluded that 

 fringing reefs do not mark stationary or rising islands as generally 

 as Darwin supposed. 



With regard to elevated reefs, the author demonstrates the 

 impossibility of explaining their featui'es by regarding them as 

 having been stationary while the ocean surface was lowered, and 

 holds that they must be due to local and diverse uplift affecting the 

 islands themselves, following on epochs of subsidence which were 

 the epochs of reef formation. The theory that such reefs were 

 formed during pauses in the elevation and emergence is considered 

 to be seriously defective, and is contrary to Darwin's views. 



The author discusses the studies of Semper on the reefs of the 

 Pelew Islands, the origin of atolls as propounded by Kein, the views 

 of Murray on barrier reefs and atolls, and of Wharton on the 

 truncation of atoll foundations ; but forms the opinion that the 



