P. A. Daly — Problems of the Pacific Islands. 175 



continent % Are the wide bays of Fiji, New Caledonia, and 

 other island groups due to this older drowning of river valleys 

 or to recent drowning, as implied in the Darwin-Dana theory ? 



5. Is that theory correct in assuming that coral growth has 

 been continuous through the latest geological periods % 



This question leads directly to my remaining topic — field 

 problems suggested by the Glacial-control theory, the other 

 explanation of reefs here to be considered. Its more elaborate 

 statement is about to appear in the Proceedings of the Ameri- 

 can Academy of Arts and Sciences.* 



Glacial-control theory of coral reefs. — During a visit to 

 Oahu and Hawaii in 1909, 1 was impressed with the small area 

 covered by each of their fringing reefs. Since corals grow 

 and add to their reefs with great rapidity, the small width of 

 the Hawaiian reefs means that they are, geologically speaking, 

 very young. The true cause of their youth was unsuspected 

 until 1 discovered the traces of a glacier at the 12,000-foot 

 contour on the slope of Mauna Kea, the highest summit of 

 Hawaii. The observed markings had a degree of freshness 

 like that of the Pleistocene glacial markings in North America 

 and Europe. The conclusion seems inevitable that the air and 

 sea temperatures of Hawaii, not many thousands of years ago, 

 were low r er than the temperatures now prevailing. Since the 

 minimum marine temperature at these islands is 23° C, only 

 3° above the lowest limit at which corals can thrive, it is an 

 obvious question whether the Hawaiian reefs were not incapa- 

 ble of active growth during the Glacial period. If they did 

 not grow vigorously, the surf would quickly destroy them. By 

 this view, then, the existing reefs are due to post-Glacial coloni- 

 zation of the Hawaiian shallows by corals. Because they have 

 enjoyed warmer water since the Glacial period, the colonists 

 and their offspring have built reefs in spite of the rolling surf. 



The open Pacific and Indian oceans nowhere have mean 

 monthly summer temperatures as high as 30° C, and, in much 

 of the coral-reef area of the globe, the winter temperature is 

 no higher than 20° to 26°. Glacialists are becoming steadily 

 more convinced that the whole earth was chilled during the 

 Glacial period. Yarious lines of evidence indicate that its 

 average air temperature was lower than now by 5° to 10°, if 

 not a little more. As the air temperature falls, that of the sea 

 surface must fall also. In the seas here considered, a drop of 

 5° to 10° in temperature would cause a partial or complete 

 destruction of the living corals. Thus pondering over the 

 Hawaiian reefs, I was led to hazard the hypothesis that the 

 Glacial period was a time of greatly inhibited reef growth 

 *See also this Journal, vol. xxx, p. 297, 1910. 



