248 DALY. 



subordinate until other borings are made at properly selected points 

 on other platforms, preferably those in the Pacific and Indian oceans. 

 (See page 218.) 



General Conclusion. 



Older than either the subsidence theory or the Glacial-control 

 theory is the view that atoll and barrier reefs stand on sea-cut plat- 

 forms, the date and conditions of the abrasion being left undecided. 

 The latest theory by no means excludes belief in the importance of 

 pre-Glacial marine erosion in preparing the reef platforms. The 

 Mesozoic and older oceanic islands and continental shores were pre- 

 sumably not always protected by reefs from the fury of the sea. If 

 not protected for one or more long periods, during which sea-level 

 was unchanged, broad wave-cut benches were inevitable. The 

 existing reef-coral species appear to have been evolved during the 

 Tertiary period. Their full cooperative power of resisting abrasion 

 could not have been reached until a time much later than that when 

 the most ancient of the species were evolved. Massive coral reefs 

 of the clearly protective type are rare in the uplifted Tertiary forma- 

 tions, and it is not certain that a single one exists in the pre-Tertiary 

 limestones. Even under existing conditions, many coral structures, 

 apparently in positions favorable to vigorous reef growth, are com- 

 pletely truncated by the waves. Other reefs are just able to hold 

 their own because of the geologically recent development of coopera- 

 tion among the coral species. It is reasonable to suppose that the 

 pre-Tertiary coasts, and perhaps the early Tertiary coasts, were less 

 well protected by reefs. On the other hand, one cannot assume 

 temperature and other conditions to have been continuously favorable 

 to vigorous coral growth, since the epoch when the required coopera- 

 tion among the coral species became a habit. More generally stated, 

 the problem illustrates once again the danger of applying the strictly 

 uniformitarian principle. 



The Glacial-control theory has been formulated in the first system- 

 ative attempt to show where and when this principle, as applied to 

 the life conditions of reef -building species, breaks down. The new 

 theory really supports the conclusions of Tyerman and Bennet (1832), 

 Wharton, Agassiz, and others, who have seen, in whole archipelagoes, 

 the independence of reef and reef platform. A weakness in their 

 arguments has been the failure to show a good reason why protecting 

 reefs were absent from most inter-tropical shores for a total time long 



