GLACIAL-CONTROL THEOEY OF CORAL REEFS. 251 



facts. One leading reason for the present publication is the writer's 

 wish to emphasize the all too common failure of writers on this prob- 

 lem to value properly the facts obtained by a host of nameless investi- 

 gators, whose results appear on hundreds of hydrographic charts. 

 Nor will years of field experience in the coral archipelagoes alone give 

 the observer the facts which more and more clearly show that the 

 history of reefs is bound up with the question of the world climate 

 during post-Tertiary time. 



The Glacial-control theory has been re-stated at length, partly 

 because it is fundamentally opposed to the older submergence theory 

 in many features of principal importance to general geology. Whether 

 these two theories should be combined is a question perhaps appealing 

 to some. In the writer's opinion there is no necessity for their combina- 

 tion in the form of a general explanation of coral reefs, and doubt 

 remains that whole archipelagoes of atolls or barrier reefs ever existed 

 before the Glacial period, though rare barriers or atolls may have been 

 developed where subsidence locally affected the floor of the Tertiary 

 ocean. 



IJNrvERSiTY Museum, Harvard University, 

 Cambridge, Massachusetts. 



