42 PROCEEDINGS OF THE PRINCETON MEETING 



The Marquesas are Recent in geologic age. The Tortugas were outlined 

 during Pleistocene submergence after an interval of uplift following Pliocene 

 deposition; after these events there was a second period of uplift, and after 

 it a second period of depression. The modern corals and the surface detritus 

 of the Tortugas rest on an older foundation shaped for them during an ante- 

 cedent period of submergence. 



The elevated barrier reef of Florida was formed during subsidence follow- 

 ing uplift subsequent to the close of Pliocene time. After its formation the 

 reef tract was elevated about 50 feet. This elevation was followed by depres- 

 sion and the present barrier formed seaward of the older one on a platform 

 already prepared for it. These conditions simulate those found on Andros 

 Island, Bahamas, and in Cuba. In the Bahamas, instead of an older Pleisto- 

 cene reef, there is Pleistocene oolite. 



The oscillations of sealevel in Florida and around Andros Island were 

 without notable tilting or flexing of the preceding deposits, while there was 

 decided differential crustal movement preceding the last depression in Cuba, 

 where the terraces rise higher at the eastern end than westward, and those 

 on the north coast west of the longitude of Manzanillo stand higher than 

 those on the south coast. 



As atolls are solely constructional geologic phenomena, Agassiz's "old ledge" 

 in the atolls of the Pacific belongs to a previous physiographic cycle, and the 

 Recent corals are growing on an older foundation. There was in the Pacific 

 a great development of coral reefs, including atolls, in Pleistocene (perhaps 

 late Tertiary) time, antecedent to the Recent reef development. These earlier 

 reefs have been subjected to differential crustal movement, so that certain 

 areas (as Makatea, Paumotus, Mango, Fijis, etcetera) have been lifted above 

 sealevel; others remain at about sealevel (Rahgiroa), while in other areas 

 (or in other parts of the same area) there has been depression (Bora Bora). 

 The Pacific island groups have not oscillated as units, but have undergone 

 differential crustal movement. 



The data presented on the relations of the barrier reefs of Florida, Bahamas, 

 Cuba, and Australia showed that all of them stand on platforms submerged by 

 rise of strand-line, and that the platforms are " independent of the limits of 

 living reefs. It is evident that the reefs are superimposed on platforms formed 

 by other than reef agencies, and that reef-building organisms grow only in 

 those places on the platforms where conditions for their life are favorable. 

 The barrier reefs of Yiti Levu, Fijis, and Tahiti, Society Islands, are similar 

 in their relations — ^that is, they are superimposed on depressed platforms, the 

 presence of which is independent of the reefs. 



The accordance in depth of the barrier-reef lagoons of Australia, the Society 

 Islands, etcetera, with that of the lagoons of oceanic atolls was indicated. 

 Attention was directed to the comparative crustal stability of the Bermuda 

 Islands and of the Paumotuan atoll region, and the conclusion expressed that 

 great crustal subsidence in atoll areas is not indicated by the facts at present 

 available. 



Eead in full from manuscript. 



The section adjourned about 5.30 o'clock p. m. 



