ABSTRACTS AND DISCUSSIONS OF PAPERS 45 



to justify a general conclusion as to relations of Recent coral-reef development 

 to glaciation and deglaciation. 



A brief comparison will now be made with the Great Barrier Reef of 

 Australia. Fifteen profiles, on the same horizontal and vertical scales, the 

 latter about 70 times the former, were drawn on the British Admiralty charts 

 across the continental shelf south of the Great Barrier Reef and across the 

 reef. These profiles show the continuity of the platform from the area south 

 of the Great Barrier, that there is an outer, deeper flat about 200 feet deep, 

 and that, except near its north end, the reef stands back from the seaward 

 edge of the continental shelf. Therefore, apparently the idea that the plat- 

 form was formed by infilling behind the reef may be permanently set aside. 

 There is striking general similarity of the conditions presented to those off 

 Nicaragua and in the West Indies. The evidence in favor of a shoreline be- 

 tween about 25 and 30 fathoms below present sealevel antecedent to Recent 

 submergence is strong, if not conclusive, and supports the deduction that the 

 living barrier reef is growing on what was a land surface in Pleistocene time — 

 an interpretation essentially that proposed by E. C. Andrews in 1902. 



The relations around the Pacific islands off which barrier reefs occur are 

 those of continuous platforms surmounted or margined by discontinuous reefs. 

 These relations indicate the superposition of reefs on antecedent platforms 

 which have undergone geologically Recent submergence. E. C. Andrews so 

 interprets the conditions of formation of the barrier reefs off the Fiji Islands. 3 

 It appears to me that the conditions governing the development of the living 

 reefs in the West Indies, Central America, Brazil, Florida, and Australia are 

 clear. The reefs have grown on antecedent basements during Recent sub- 

 mergence. The history of these basements is complex, but during Pleistocene 

 time they stood higher with reference to sealevel than now ; their outer mar- 

 gins were remodeled by marine cutting and marine planation, and they were 

 then resubmerged. These changes in height of sealevel accord with the de- 

 mand of the glacial control theory. It would be remarkable if the conditions 

 in the tropical western Pacific Ocean were exceptional, and the present avail- 

 able facts indicate that they conform to the principles governing reef develop- 

 ment in the other areas. Here it should be said, regarding the charts for the 

 Pacific, that as they have been made primarily for navigation purposes, the 

 depths of lagoons and lagoon channels are often given in a way fairly satis- 

 factory, but on only a few charts can the submarine profiles outside the reefs 

 be determined. The coral-reef problem can not be regarded as satisfactorily 

 solved until the relations in the Pacific islands have been ascertained. In my 

 opinion, but little further advance in understanding the problem can be ex- 

 pected from purely biologic studies or from physiographic investigations of the 

 dry land surface alone. As apparently the greatest present need is for more 

 accurate information on the detailed submarine relief in depths between 15 

 and 50 fathoms, especially on the seaward .margins of the platforms, both 

 outside the reefs and off the breaks in the reef lines, the efforts of those 

 interested in such investigations should be concentrated on getting additional 

 hydrographic surveys in coral-reef areas. 



Presented by title in the absence of the author. 



3 Am. Jour. Sci., vol. 41, Jan., 1916, pp. 135-141. 



