208 THE BERMUDA ISLANDS. 



(Bermuda) 0'036; Madrepora aspera 0'073; Porites plavaria 

 (Bermuda) 0"093 ; weathered oyster-shells, 0'331 ; crystallized 

 carbonate of lime, 0123 ; amorphous carbonate of lime, 0"649. 

 The rate of solution here given is vastly in excess of the results 

 obtained by Mr. Ross. 



J. Hurray. " On the Structure and Origin of Coral Reefs and Islands." Proc. 

 Royal Soc. Edinburgh, X, 1880. 



An exposition of the non-subsidence or accretion theory of 

 the formation of coral structures. The author thus sums up 

 his conclusions (p. 517)': 



1. Foundations have been prepared for barrier reefs and 

 atolls by the disintegration of volcanic islands, and by the 

 building up of submarine volcanoes by the deposition on their 

 summits of organic and other sediments. 



2. The chief food of the coral consists of the abundant 

 pelagic life of the tropical regions, and the extensive solvent 

 action of sea-water is shown by the removal of the carbonate 

 of lime shells of these surface organisms from all the greater 

 depths of the ocean. 



3. When coral plantations build up from submarine banks 

 tiiey assume an atoll form, owing to the more abundant supply 

 of food to the outer margins, and the removal of dead coral 

 from the interior portions by currents and by the action of the 

 carbonic acid dissolved in sea-water, 



4. Barrier reefs have built out from the shore on a foundation 

 of volcanic debris or on a talus of coral blocks, coral sediment, 

 and pelagic shells, and the lagoon channel is formed in the 

 same way as a lagoon, 



5. It is not necessary to call in subsidence to explain auy of 

 the characteristic features of barrier reefs or atolls, and all these 

 features would exist alike in areas of slow elevation, of rest, or 

 of slow subsidence. 



The above constitute the main propositions of what is fre- 

 quently termed the " Murray theory " of the formation of coral 

 structures. These have already been discussed in the chapter 

 on " The Coral-Reef Problem," and therefore call for no special 



