182 P. A. Daly — Problems/)/ the Pacific Islands. 



the waves and currents of the Glacial period. Section 31, 

 across one corner of the Seychelles bank (Indian ocean), is 

 thirty-five miles long. Sections 32 and 33, of the Macclesfield 

 bank (China Sea), are drawn to the same scale. For some 

 reason or reasons these banks have not been favorable to the 

 vigorous growth of reefs, though there are reef-covered plat- 

 forms in the vicinity of each bank. Transitional types are 

 exemplified in the Turpie bank, north of Fiji, on which there 

 is a reef rim only on one side and that covered by 100 and 120 

 feet of water. The bank is twenty-five miles long, a platform 

 of medium size. 



Since the Glacial period closed at a time variously estimated 

 as from 20,000 to 50,000 years ago, all existing reefs should be 

 comparatively narrow. From the known rates of coral growth 

 one can easily calculate the maximum width possible during 

 50,000 years of growth. The result is to show that the area 

 of a reef on a wide platform must be relatively minute, when 

 compared with that of its lagoon ; and that the width of barrier 

 or atoll reef is to be measured in hundreds of yards rather than 

 in miles. In fact, the charted soundings display full evidence 

 of this kind as to the youth of all oceanic reefs. 



The problem of the coral reef is thus seen to be, in essence, 

 the problem of the platform. As the Glacial-control theory is 

 specially concerned with the platforms, it suggests many ques- 

 tions relating to the origin of the island platforms in the 

 Pacific ; and, again, as the field worker answers them, he 

 accumulates precious facts bearing on the history of the earth's 

 tropical zone as a whole. Some of these questions are here 

 enumerated. 



1. What degrees of antiquity are shared by the volcanoes of 

 the Pacific floor ? If many of its reef platforms are due to 

 the erosion of great volcanic islands, such erosion must have 

 largely antedated the Glacial period. If the islands were very 

 old, they must have been worn down close to sea-level by con- 

 stant weathering and stream action. When so reduced, the 

 residual rock must ultimately undergo deep decay. Hence for 

 two reasons — low altitude and weakening of the rocks — very 

 old islands are easily truncated by attacking ocean waves. An 

 important object of future investigators in the Pacific would 

 be to search for evidence bearing on the dates of island forma- 

 tion. There is no reason why volcanic islands may not have 

 been there formed in the ancient periods of Paleozoic and pre- 

 Cambrian time. Observations on the depth to which weather- 

 ing has affected the integrity of the older islands are needed, as 

 they bear on the question of the speed of wave abrasion. 



2. In the many memoirs published on the coral-reef con- 

 troversy, almost no emphasis has been placed on the point as 



