CORALS Al^B CORAL REEFS VAUGHAIST. 235 



the recognition of the fact tliat booivs, papers, inkstands, etc., are on 

 the top of a desk does not require knowledge of the process of manu- 

 facture of the desk or even of the material out of which it is made ; 

 and that one geologic formation overlies another may be ascertained 

 without having complete knowledge of the geologic histor\^ of either 

 the overlying or the underlying formation. 



That the origin of the submarine flats on which offshore reefs 

 stand should be understood is important in the advancement of our 

 knowledge of geologic historj'^, and I have acquired as much in- 

 formation on the subject as I could. I am convinced that there 

 is no one explanation that can be applied to all of them. The fol- 

 lowing kinds of flats have already been recognized: (1) Slightly 

 tilted bedded tuffs, as in the fossil reefs of Antigua; (2) slightly 

 tilted bedded limestones, as off the south coasts of St. Croix and 

 Cuba; (3) submerged coastal flats, as in the Fiji Islands; (4) sub- 

 merged peneplained surfaces, as in the fossil reefs of Porto Rico; 



(5) submarine plains due to uplift of considerable areas of the 

 ocean bottom and to the deposition of organic deposits on such a 

 surface, as the Floridian Plateau prior to the formation of the 

 middle and upper Oligocene reefs of Florida and southern Georgia ; 



(6) flats of complex and not definitely known origin, such as those 

 of the Antigua-Barbuda Bank, the Virgin Bank, and the continental 

 shelves of tropical America and Australia.^ Plains suitable for the 

 growth of corals have been formed by subaerial and submarine depo- 

 sition, and by both subaerial base-leveling and submarine planation. 

 Nearly every, if not every, plain-producing process operative in 

 tropical and subtropical regions has taken part in the formation of 

 plains on which coral have grown or are growing where the plains 

 have been brought below sea level and where the other ecologic con- 

 ditions for offshore reef formation obtain. Although, as regards 

 coral reefs, I wish to emphasize the independence of those platforms 

 concerning which information is available, I wish also to make 

 it clear that I recognize that in-filling does take place behind reefs, 

 but that such in-filing is not sufficient in amount to account for the 

 flats above the surfaces of which the reefs stand. 



The Glacial Control theory will now be considered in more detail. 

 If this theory is true the following conditions should now prevail: 



^ Professor Davis, in an article entitled " The Great Barrier Reef of Australia," pub- 

 lished in the Amer. Jour. Sci., 4th ser., vol. 44, pp. 339-350, November, 1917, proposes 

 the hypothesis that the platfoi-m on which the living Great Barrier Reef is growing 

 resulted irom in-filling behind a barrier until a " mature reef-plain," according to his 

 terminology, was formed. Although this is an interesting hypothesis, it is at present 

 not possible to procure decisive information on the processes wherebj the Australian 

 continental shelf was produced. 



