34 vaughan: geologic history of coral reefs 



due mostly, if not solely, to the intolerance of such organisms to 

 sedunent. Certain of my experiments show conclusively that, 

 if the colonies are protected from sediment, the growth of corals 

 within a lagoon may exceed that of corals on the outside. The 

 possibilities of a basement attaining the proper depth, where the 

 other necessary vital conditions prevail, are numerous and need 

 not here be recapitulated. 



As bearing on the relative stability of one so-called coral island, 

 it will be stated that Dr. Jos. A. Cushman has found Nummulites 

 in the borings from the Bermuda deep well at depths from 131 

 to 193 feet, or, expressed in fathoms, from 22 to 32 fathoms below 

 sea level. As these fossils indicate either a lower Oligocene or 

 an upper Eocene age for that part of the bore, it is evident that 

 crustal changes in the Bermudas since that time have been slight. 

 Relative crustal stability for the Paumotus has been indicated. 

 Daly's compilation of the depth of atoll lagoons is most signifi- 

 cant, as it shows accordance in depth with the lagoons of barrier 

 islands. Whether or no his hypothesis of the rise of sea level 

 to an amount of about 30 fathoms in the tropics, due to the dis- 

 appearance of glaciers, be accepted, it at least is evident that 

 great crustal subsidence for atoll areas is not indicated by the 

 facts at present available. ^ 



^ This paper is an abstract of data and conclusions bearing on the coral reef 

 problem from the following publications by the writer: 



A contribution to the geologic history of the Floridian Plateau. Carnegie 

 Institution of Washington, Publication 133, 99-185, 15 pis., December, 1910. 



Remarks on the geology of the Bahama Islands and on the formation of the 

 Floridian and Bahaman oolites (abstract). Jour. Washington Acad. Sci., 3, 302, 

 303, May 19, 1913. 



Preliminary remarks on the geology of the Bahamas, with special reference to 

 the origin of the Bahaman and Floridian oolites. Carnegie Institution of Wash- 

 ington, Publication 182, 47-53, 1914 (in press). 



The building of the Marquesas and Tortugas atolls, and a sketch of the geo- 

 logic history of the Florida reef tract. Idem, 55-67, 1914 (in press). 



To the abstract of discussions included in the papers cited are added a more 

 general account of barrier reef platforms and some remarks on atoll rims that 

 margin the fiat summits of eminences rising from oceanic depths. 



