176 DALY. 



Moreover, it is not certain that, after the cooperative reef-building 

 habit was well established, the tropical-sea temperature was not for a 

 time too high for vigorous growth of reef corals. Mayer's experiments 

 have led him to conclude that these would be killed if the ocean tem- 

 perature were as high as 98° F. (36.7° C). According to some of the 

 experiments certain species ceased to take food at temperatures below 

 98° F.24 This temperature is only 12° F. (6.7° C.) higher than that 

 of the warmest surface water of the present ocean. The c^uestion 

 arises as to the tropical-sea temperatures during that part of Tertiary 

 time when Grinnell Land, at 81° 44' N. Lat., had a mean July tempera- 

 ture about 27° F. higher than it enjoys now, while the mean January 

 temperature was then at least 50° F. higher than now.^^ Of course 

 one cannot assume that the tropical sea was then correspondingly 

 warmer than at present, but the possibility of a temporary lowering 

 of vitality in the reef corals through excessive heat cannot be easily 

 dismissed. 



More certain is the fact that, though Tertiary coralliferous lime- 

 stones of great extent and thickness appear in Fijian and other up- 

 lifted islands, no very wide, typical coral reefs appear yet to ha^■e been 

 found among them.^^ 



Thus, the idea is to be entertained that massive coral structures of 

 Tertiary or earlier age did not greatly retard wave abrasion during the 

 Glacial period. 



The degree to which the rocks of the oceanic islands were weakened 

 by deep weathering during pre-Glacial time varied with the antiquity 

 of those islands. They certainly had very different dates of origin. 

 Like all the continents, the area of the tropical seas was probal)ly 

 affected b^,' strong ^'olcanic action in the early pre-Cambrian, as well 

 as occasionally through all subsequent time. Presumably the major- 

 ity of the Pacific-floor volcanoes are pre-Pliocene, if not pre-Tertiary 

 in age. If this be true, the oldest volcanic islands, long before the 



24 A. G. Mayer, Pop. Sci. Monthly, Sept., p. 219 (1914). 



25 According to J. Haun, Handbook of Climatology, trans, by R. DeC. Ward, 

 New York, 1,375 (1903). 



26 li. B. Guppy (Observations of a Naturalist in the Pacific l)et\veen the 

 years 1S96 and 1899, London, 1, 7 (1903)) concluded that coral reefs do not 

 appear to have existed in \'anua Levu (Fiji) when that island began its 2,000- 

 foot uplift. He also notes that "coral reefs never have been very extensive 

 at the sea-border during the last stages of emergence" of that island. The 

 dating of the Vanua Levu uplift is evidently a matter of great importance, 

 on which, however, information is scant. It doubtless began long before the 

 Glacial period. 



