224 



ANNUAL REPOET SMITHSONIAN INSTITUTION, 1917. 



3. The third theory can not be referred to any one man, as it has 

 gradually grown out of the work of many men. Briefly stated it is 

 that offshore reefs have formed on antecedent flattish basements or 

 platforms, during or after submergence, in areas where the ecologic 

 conditions are favorable for the life of reef-building corals. Some of 

 the work of i\.lexander Agassiz, H. B. Guppy, and R. T. Hill pre- 

 pared the way for this interpretation, but apparently it was first 

 definitely made b}^ E. C. xindrews^ as a result of his study of the 

 Great Barrier Reef of Australia, and subsequently Hedley and 

 Griffith Taj'lor corroborated his conclusions. Later ray own studies 

 in Florida, the "West Indies, and Central America led me to make for 

 those areas essentially the same interpretation as that of Andrews 

 and Hedley and Griffith Ta^dor for the Australian Great Barrier. 



Fig. 8. — Reproduction of J. B. Jukes's section across the Great 

 Baruieu Reef of Australia, a. Sea outside tub barrier, gen- 

 erally unfathomable, h. Tub actual barrier, c. Clear channel 



INSIDE THE BARRIER, GENERALLY ABOUT 15 OR 20 FATHOMS DEEP. 

 d. The INNER REEF. 6. ShOAL CHANNEL BETWEEN THE INNER REEF AND 

 THE SHORE. F. THE GREAT BUTTRESS OF CALCAREOUS ROCK, FORMED 

 OF CORAL AND THE DETRITUS OF CORALS AND SHELLS. O. THE MAIN- 

 LAND, FORMED OF GRANITES AND OTHER SIMILAR ROCKS. 



3a. The validity of the theory next to be considered, the Glacial 

 Control theory, is dependent on the soundness of the conclusions ex- 

 pressed in the preceding paragraph. This theory, as is the case with 

 most theories, grew gradually, and ultimately found one chief ex- 

 ponent, who is R. A. Daly.^ Of course taking w^ater from the ocean 

 to form the continental glaciers of Pleistocene time would lower 

 the level of the surface of the sea during that time to an amount equal 

 to the quantity of water abstracted from the ocean, if there Avere no 

 crustal movements, such as down-bending due to the weight of the ice 

 caps in high latitudes, that would counteract the effects produced by 

 removal of water from the ocean to form the great ice caps. During 

 Pleistocene time, because of the cold climate of that time, the rate of 

 formation of coral reefs was probably reduced, and, as the protection 

 they afforded shores was thereby lessened, the waves of the sea would 

 then cut extensive submarine plains. With the return of warmer 



^ Preliminary note on the geology of the Queensland coast with reference to the 

 geography of the Queensland and N. S. Wales plateau : Linn. Soc. New South Wales, 

 pt. 2, pp. 146-185, 1902. 



» The Glacial-Control theory of coral reefs : Amcr. Acad. Arts and Sci. Proc, vol. 51, 

 pp. 157-248, 1915. 



