Daly — The C oral-Reef Zone. 137 



The coral-reef problem now specially needs the atten- 

 tion of geologists, the zoologists having largely furnished 

 their share of the required data. Unfortunately, few 

 geologists have had the opportunity to study reefs in the 

 field or to absorb the information embodied in modern 

 ocean charts and the facts recently acquired by the 

 oceanographers. The geologist's task is, moreover, one 

 of peculiar difficulty. His main endeavor should be to 

 picture the coral-reef areas through their long past ; yet 

 much of the record is hidden beneath the sea. His recon- 

 struction of past geography depends on the wise 

 application of his knowledge of present conditions and 

 processes ; yet present conditions and processes them- 

 selves are to a greater or less extent inherited and 

 therefore only to be thoroughly understood by sound 

 inference. Here, as elsewhere in geology, progress is 

 directly proportional to the advance of properly con- 

 trolled speculation.- 



Much of the voluminous literature on the coral-reef 

 problem has little value because authors have not insist- 

 ently done their utmost to imagine the tropical geog- 

 raphy at stages preceding the present, that is, to think 

 geologically. Or, if they have made the attempt, some 

 authors have nevertheless too literally applied the 

 uniformitarian principle. For example, it has been 

 assumed that reef corals and associated organisms have 

 thriven for an indefinitely long time as they do now ; or 

 that general sea-level has been essentially constant for a 

 large part of geological time ; or that the tropical climate 

 has been nearly constant during the Cenozoic era. Of 

 course no one can yet reconstruct adequately the Paleo- 

 zoic, Mesozoic, or even Tertiary physiography of the 

 tropical belt, though certain elements are becoming 

 clearer. The attempt to visualize conditions obtaining 

 in the (Pleistocene) Glacial period, particularly with 

 respect to the development of coral reefs, is more hopeful. 

 The following paper sketches the conditions, as inferred 

 with more or less probability, from ascertained facts. 

 It is also intended to supplement a detailed discussion 

 already (1915) published. 1 A new statement seems war- 

 ranted, partly because the writer's views have not been 

 thoroughly understood, and partly because some aspects 



1 The Glacial-control Theory of Coral Eeefs. Proc. Amer. Acad, of Arts 

 and Sciences, vol. 51, pp. 157-251, 1915. See also, this Journal, vol. 30, pp. 

 297-308, 1910. 



