136 Daly— The Coral-Beef Zone. 



Art. X. — The C 'oral-Reef Zone During and After the 

 Glacial Period; by Reginald A. Daly. 



Introduction. 



Duration and subdivisions of the Glacial period. 



Shores and shoals at the beginning of the Glacial period. 



Coral reefs at the beginning of the Glacial period. 



Conditions during the Glacial period. 



Glacial controls over reef growth. 



Objections to the Glacial-control theory of the living reefs v 



Evidence from drowned valleys. 



General absence of spur-end cliffs. 



Evidence from cliffed islands. 



Depths of lagoons. 



Crustal movements in areas near coral reefs. 



Assumed uniformity of reef growth. 



Additional objections. 

 Summary. 



Introduction. 



A full understanding of the living coral reefs would 

 mean the conquest of a problem which still demands 

 a huge increase in our knowledge of the principles and 

 facts of oceanography, dynamical geology, and historical 

 geology. Hence this particular problem is a stimulus to 

 further field investigations of most diverse character 

 and of profound importance. Examples are : the quan- 

 titative study of wave abrasion, current abrasion, shelf- 

 building, organic deposits, bottom growths, and the 

 physical conditions of life for many marine species of 

 animals and plants ; the origin and initial dates of conti- 

 nental shelves, of the islands composed of continental 

 rocks, and of deep-sea volcanic islands and shoals ; the 

 quantitative study of subaerial erosion in the tropics ; the 

 evolution of marine species; the geological history of 

 climate in the tropics. This many-sided character is well 

 illustrated in the superb Murray Island volume recently 

 published by the Carnegie Institution of Washington, 

 under the direction of Dr. A. Gr. Mayer. 



On the other hand, final success in the attack would 

 deeply affect the outlook for answers to such questions 

 as those relating to: the stability of the earth's crust; 

 "land bridges'' and the dispersal of organisms; the 

 origin of the ocean basins ; interpretation of ancient 

 limestones and dolomites ; shore-line development ; the 

 processes of sedimentation in general. 



