R. A. Daly — Problems of the Pacific Islands. 183 



to when the oceanic islands began to be well protected by reef 

 corals against the surf. Yet paleontologists tell us that the 

 Madreporaria, the reef-builders par excellence, were first 

 developed during the Mesozoic era ; that very few of the coral 

 species in the present reefs are found, as fossils, in formations 

 earlier than the Miocene ; and that practically none seems to 

 have been evolved in pre-Tertiary time. Moreover, a reef's 

 ability to resist abrasion depends on a kind of co-opera- 

 tion among the reef species. Such power of co-operation 

 must come later than the evolution of individual species of 

 corals. Before it was developed to the required degree, 

 the islands were subject to complete truncation by waves dur- 

 ing an indefinite number of geological periods. With future 

 researches as to the antiquity of the reef faunas should be 

 associated an investigation of the exact reasons why reef 

 organisms can now resist the fury of the breakers. 



3. Even after the co-operative reef fauna was evolved, there 

 is no certainty that it has always continued to protect the 

 islands. A. G. Mayer has recently shown the serious injury 

 done to reef corals by raising the temperature of the water to 

 35° oi' 36° C. This is only 6° or 8° above the temperature of 

 the warmest water now bathing most of the coral islands. 

 During at least one Tertiary stage, the earth enjoyed a semi- 

 tropical climate in Grinnell Land, only a few hundred miles 

 from the North Pole. At that time the intertropical area may 

 well have been too hot for vigorous coral growth. If so, the 

 intertropical islands were unprotected and subject to prolonged 

 abrasion by the waves. One of the questions raised is : Does 

 the paleontology of the Pacific islands show a failure of thriv- 

 ing reef corals during the Tertiary period ? The need of 

 further observations on the temperature range of living corals 

 and of their reef-building allies is evident and vital. 



4. The pre-Glacial truncation of islands was of course 

 accompanied by the formation of offshore embankments. 

 Both phases of this marine w T ork need quantitative scrutiny. 

 To how great a depth can waves of the open ocean erode bed- 

 rock with sensible speed? This is a question not yet answered, 

 for the studies so far made refer to waters like the border seas 

 of Europe, where the ocean swell loses power by running over 

 wide shallows before reaching the cliffs. Direct observations 

 on shores of volcanic islands in the midst of the deep Pacific 

 would be highly valuable. 



Similar studies are desirable as to the depths at which the 

 major ocean currents can move bottom sediment. To this 

 action the slow development of the continental and island 

 shelves, so far as they are detrital in origin, is attributed. A 

 required datum is the measured speed of open-ocean currents 

 at varying depths. Such measurement is possible from a 



