CORAL REEFS 177 



1,114 feet. The core of this bore was carefully preserved 

 and brought to this country where it was examined from 

 end to end by scientists in order to find out what it was 

 composed of and, most important of all, whether it was 

 formed throughout of coral limestone or whether that 

 was succeeded by some different material in the lowest layers. 

 This examination showed that the bore was composed 

 throughout of the one substance, coral limestone, and this 

 was at once claimed by the advocates of the Darwin theory 

 as a vindication of their views. But now enters a complica- 

 tion for, without denying that the bore was composed 

 throughout of rock of coral origin, Murray and his adherents 

 stated that this was due to the fact that the bore, instead 

 of going through the centre of the reef, had been made 

 through the edge and so had passed through the talus of 

 coral fragments which had broken off the edge of the growing 

 reef and fallen into deep water. 



And there the matter very largely rests. Probably both 

 theories are correct for certain cases and there is no 

 universally applicable explanation of the formation of 

 coral reefs. The whole point, as we hope has been made 

 perfectly clear, is the way in which the conditions — very 

 clearly defined and well-known — necessary for the growth 

 of corals are provided. Before we close this chapter, 

 however, a short reference must be made to a more recent 

 theory put forward by Professor Daly of Harvard, and 

 which, whatever the amount of truth it contains, is of 

 exceptional interest. Known as the " glacial-control " 

 theory, this states that during the great ice ages so much 

 water was locked away in the form of ice that the surface 

 of the sea was lowered by between twenty-five and thirty- 

 five fathoms in the tropics. During this period the pre- 

 existing coral reefs (for coral reefs are known from the 

 earliest times of which we have any geological evidence) 



