GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 305 



SUBMERGED BANKS NORTH OF THE CORAL REEF ZONE IN THE WESTERN ATLANTIC 



OCEAN. 



That there are on" the Atlantic coast of Central and North America, 

 north of the temperature zone in which coral reefs now exist, sub- 

 marine banks at suitable depth below sea level for the growth of reef- 

 forming corals, has been stated in several of my papers. 1 There are 

 six submarine banks projecting seaward from the eastern part of 

 Central and North America. Named in order from the south north- 

 ward these banks are, first, three on which there are coral reefs, 

 namely, Mosquito Bank off Nicaragua and Honduras, Campeche 

 Bank off Yucatan, and the Floridian Plateau; and, second, three on 

 which there are no coral reefs, namely, Georges Bank, the banks off the 

 coast of Nova Scotia, and the Grand Banks of Newfoundland. The 

 presence of such banks is entirely independent of corals, but corals 

 will grow on the surface of such banks where the necessary ecologic 

 conditions prevail. 



SUMMARY OF THE CONDITIONS UNDER WHICH THE AMERICAN FOSSIL AND LP7ING 



CORAL REEFS FORMED. 



1 . The elevated Pleistocene fringing reefs of the West Indies are 

 separated by erosion unconformities at their bases from the geologic 

 formations that they overlie, but they were usually, if not invariably, 

 formed during intermittent uplift following considerable depression. 



2. The offshore reefs, whether forming parts of more or less bedded 

 formations or forming patches, stacks, or barriers of living reef, were 

 formed during or after submergence, as is shown in the case of the 

 fossil reefs by unconformable basal contacts wherever basal contacts 

 could be studied, and in the case of the living reefs by a great variety 

 of evidence indicating geologically Recent submergence. 



3. The offshore reefs grew upon or are growing upon antecedent 

 flats, only a small part of the surface of which was or is covered by 

 reefs. The flats existed prior to the submergence during or after 

 which the reefs developed. Corals are constructional geologic agents 

 and help build up the sea bottom, but the large flats on which they 

 grow would exist were there no corals. Such flats are not confined 

 to the temperature zone in which corals live. 



4. The submergence of the basements of the fossil reefs seems more 

 reasonably explained as the result of differential crustal movement; 

 but the development of the living reefs seems in large part a result 

 of geologically Recent rise in the stand of ocean level, for nearly the 

 entire eastern shore of the Americas from Argentina on the south to 

 Cape Cod on the north exhibits evidence of Recent submergence, after 

 which there has been in some places minor emergence by differential 

 crustal movement. The amount of the submergence usually seems 



i Science, new ser., vol. 41, pp. 508, 509, April 2, 1915; Geol. Soc. Amer. Bull., vol. 26, pp. 58-60, 1915; Amer 

 Journ. Sci., ser. 4, vol. 41, p. 134, 1916; Carnegie Inst. Washington Yearbook No. 14, p. 238, 1916. 



