424 



SCIENCE PROGRESS 



whether now at sea-level in the process of formation or elevated 

 above sea-level since their formation, appear to lie, as far as 

 known, with striking unconformity on strongly eroded founda- 

 tions. Hence the foundations, mostly volcanic islands, must 

 have suffered erosion during a considerable period before they 

 were submerged, in preparation for the unconformable deposi- 

 tion of the reef limestone upon them. Surely no geologist can 

 hesitate to adopt this conclusion, if the facts of structure are 

 as stated. 



Furthermore, inasmuch as most fringing reefs which front 

 the open sea in a narrow belt around their island lie, like the 



H 



Fig. i.— Sector diagram, illustrating successive stages in the formation of coral reefs around 



a subsiding volcanic island. 



As a result of subsidence, the dissected volcano must have an embayed shoreline, as in sectors j and k ; and 

 the lagoon deposits of barrier reefs and atolls must lie uncomformably on the eroded surface of the 

 submerged slope, as in section M. The central islands within barrier reefs usually exhibit the features 

 here drawn, but their bays are more or less filled with deltas, and their points are bordered by fringing 

 reefs. A number of uplifted reefs are known to rest unconformably on a slanting and eroded foundation, 

 as in section m. 



fringing reefs that commonly occur around a central island 

 within a barrier reef, unconformably upon a strongly eroded 

 volcanic surface, it must be concluded that fringing reefs do 

 not mark stationary or rising islands as generally as Darwin 

 supposed ; but it is well to remember that Darwin had two 

 views regarding reefs of this kind. The view to which he gave 

 the most emphasis, and which is commonly associated with 

 his theory of intermittent subsidence, was, as just implied, that 

 fringing reefs are formed on stationary or rising islands. But 

 he also announced another view, as follows : " If during the 

 prolonged subsidence of a shore, coral-reefs grew for the first 



