228 CORALS 



extent of about 30 fathoms. By this means large areas of 

 sea-bottom were exposed which hardened to form hmestones 

 of varying constitution. As the ice melted and the sea- 

 level rose these areas were again submerged and planed 

 down to form the submarine platforms upon which, sub- 

 sequently, the new coral reefs were formed. 



If it could be definitely proved that during the Glacial 

 Period in the northern hemisphere there was so much more 

 water stored up in the form of glacial ice than there is at 

 the present day as to cause a fall in the sea-level of 30 

 fathoms, there would be some foundation for this theory. 

 But the evidence on that point appears to be far from 

 conclusive. Moreover, the theory also demands that the 

 submarine platforms on which the coral reefs rest should all 

 be of the same (pleistocene) geological age, and evidence 

 bearing on this point can only be obtained by the study of 

 the foundations of reefs that have grown and subsequently 

 been raised above the sea-level since that period. It may be 

 some years before a sufficient survey of these upraised reefs 

 in many parts of the world has been made to judge fairly of 

 the evidence they afford on the glacial control theory, but 

 Wayland Vaughan has shown that the great Florida plateau 

 has existed since late Eocene times and that some of the 

 West Indian platforms are at least as old.^ 



The glacial control theory is extremely interesting and 

 ingenious, but it does not appear to be likely to supersede 

 entirely the other theories that have been briefly described. 

 It may be proved that " glacial control " had some effect 

 in producing the general structure and distribution of many 

 of the modern and recently upraised reefs, but there can be 

 little doubt that some of our modern reefs do not rest on a 

 submarine platform formed in post-glacial times and that 

 others rest on platforms that were certainly pre-glacial. 



The conclusion that must be reached after a careful 

 study of the literature bearing upon the subject is, that 

 there is no general agreement among men of science upon 

 any one theory of the origin of coral reefs. The controversy 



' T. Wayland Vaughan, S))iitlisojiiiui histitidioii, Bull. 103, 1919. This 

 paper contains an admirable summary of coral reef theories. 



