Transactions. 



Art. II. — The Significant Features of Reef-bordered Coasts. 



By W. M. Davis, Harvard University, Cambridge, Mass., U.S.A. 



[Read hejore the Wellington Philosophical Society, 16ih October, 1918 ; received bi/ Editor. 

 16th October, 1918; issued separately, Uth May., 1919.] 



In recognition of the honour conferred by the New Zealand Institute in 

 adding me to its list of honorary members, and in return for the kind 

 reception given me at its meetings during my Pacific journey in 1914, I 

 desire to offer the following notes for publication in its Transactions, in the 

 hope that they may aid students of coral reefs in observing certain features 

 of significance in connection with the origin of those extraordinary struc- 

 tures. References are appended to a number of my articles, the product 

 of observation, reading, and refiection during five years past, where certain 

 aspects of the coral-reef problem are treated more fully than they can be 

 here. 



Sea-level Coral Reefs are silent as to their Origin. — The corals and other 

 organisms of a sea-level reef are tru.ly of marvellous interest, and from a 

 zoological point of view merit all the attention they have received ; but 

 when a reef is examined from a geological point of view its organisms are 

 found to be reluctant, not to say incompetent, witnesses as to the manner 

 of its formation. An observer may sail along the front of a reef, wander 

 over its surface, or row about in its lagoon, and discover many facts regard- 

 ing the varied forms of life there visible, and regarding the processes, 

 organic and inorganic, now in operation ; but, apart from such factors as 

 the temperature and the depth of sea-water at which reef-building corals 

 grow, he can learn little, if anything, about the past conditions under which 

 the reef has been developed, so long as his study is directed to the reef 

 alone. 



On atoll reefs there are, indeed, no facts visible at the surface by which 

 the various theories of the origin of coral reefs can be tested : it is only 

 from borings m sea-level atolls or from natural sections of elevated atolls 

 that competent testimony as to their origin can be gained. In this con- 

 nection it may be noted that the interpretation of the Funafuti boring 

 recently published by Professor E. W. Skeats, of Melbourne (1918),* gives 

 a much better statement of its evidence as to the origin of that atoll than 

 is to be found in the original report published by the Royal Society, which 

 was almost silent as to the meaning of the facts that it set forth so minutely. 



Fringing and barrier reefs are, on the other hand, associated with the 

 coasts of land-masses, which may yield much information as to the past 

 conditions and processes of reef-formation, if the geological structure and 

 the physiographic development of the coastal slope are examined. For these 

 reasons it is to the coasts of the land-masses which fringing or barrier reefs 

 adjoin that attention is here chiefly directed. 



Coasts of EMERaENCE and of Submergence. 



The general features of coasts on which coral reefs occur — either fringmg 

 reefs alone, or fringing reefs in the lagoons enclosed by barrier reefs — give 

 helpful indications of the relative changes of level that the coasts have 



* For references see p. 30. 



