GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 245 



9. Hedley and Griffith Taylor ^ accepted Andrews's interpretations 

 and clearly showed that coral reefs of either atoll or linear form that 

 rise above shallow platforms owe their shapes to prevailing winds and 

 currents. They say: 



This explanation differs from that of Sir J. Murray, who considers the atoll form to 

 be assumed by abundant growth of well-fed corals on the margin and the solution of 

 dead coral rook in the interior. But if solution be so destructive, how can a reef form 

 at all? 2 



10. According to Daly^ the depths in the drowned valleys within 

 barrier reefs, in barrier-reef lagoons, and in atoll lagoons in the Pacific, 

 are closely accordant and he attributes this accordance to Recent rise 

 of sea level subsequent to deglaciation, whereby the depth of water 

 in the Tropics was increased some 33 to 38 fathoms, thus submerging 

 antecedent platforms of marine planation. That glaciation and 

 deglaciation effect the development of living reefs did not originate 

 with Daly, but it is principally he who has elaborated the hypothesis. 

 He gives in his papers an account of the earlier suggestions. 



11. Wood Jones ^ considered sedimentation the critical factor in 

 coral-reef theory, as corals grow only where there is comparatively 

 little deposition of sediment. He accepts the conclusions of Hedley 

 and Griffith Taylor on the importance of winds and currents in shap- 

 ing atolls, and especially attacks the hypothesis of "a. deepening or 

 widening of the lagoon by a process of 'solution'." 



Although the results of my own investigations will be elaborated 

 on subsequent pages, the following summary statement may here be 

 made: I have greatly multiplied the evidence in favor of Recent 

 submergence in the coral-reef areas in the western Atlantic, the Gulf of 

 Mexico, and the Caribbean Sea, and have shown that the living off- 

 shore reefs in those areas formed either during or after submergence 

 and are growing on submerged basement platforms where conditions 

 are favorable for the life of reef -forming corals. The platforms are 

 continuous beyond the limits of the reefs and their existence is in no 

 wise dependent upon the presence of reefs. 



I have also shown that the great Florida Plateau has existed as a 

 plateau since at least late Eocene time; and that some of the West 

 Indian platforms are about as old. As these plateaus existed previous 

 to Pleistocene time they could not have been formed by marine plana- 

 tion during Pleistocene glaciation. Whatever be the cause of shift 

 in position of strand line, off-shore reefs form on shallow submarine 

 flats during or after rise in sea level, provided the rate of movement 

 be not too rapid. This explanation applies to the fossil reefs of 



1 Hedley, C, and Taylor, T. Grif&th, Coral reefs of the Great Barrier, Queensland, Australasian Assoc. 

 Adv. Sci., Adelaide Meeting, pp. 397-413, 1907. 



2 Idem., p. 407. 



3 Daly, R. A., Pleistocene glaciation and the coral-reef problem, Amer. Joum. Sci., ser. 4, vol. 30, pp. 

 297-30S, 1910; The Glacial-control theory of coral reefs, Amer. Acad. Arts and Sci., vol. 51, pp. 157-248, 1915. 



* Jones, F. Wood, Corals and Atolls, London, 1910. 



