246 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



Florida and the West Indies as well as to the reefs living to-day. 

 I have pointed out that there are in the Virgin and northern Leeward 

 Islands and off the shores of Central America certain submarine 

 terrace fiats, one at a depth of about 17 to 20 fathoms, another at a 

 depth of about 26 to 30 fathoms, the deeper fiat being separated from 

 the shallower by an escarpment. These relations accord with the 

 demands of the Glacial-control theory as expounded by Daly. 



Tests of Coral-reef Hypotheses. 



The tests of the theories comprise ascertaining the answers to the 

 following questions: 



1. Were the important coral reefs of the world formed during or 

 after the submergence of their basements, either by a sinking of the 

 land or by a rise of ocean level due to some world-wide cause ? 



2. What is the rdle of corals as constructional geologic agents "i 

 What percentage of the sediments around coral reefs is composed of 

 corals, and is the flat area between a barrier reef and the shore due 

 to infilling behind the reef or was there a shallow marginal fiat before 

 the reef formed ? 



3. Can a lagoon channel behind a barrier reef or the lagoon within 

 an atoll rim be formed by submarine solution by sea water or by 

 submarine scour ? 



4. What and how much effect have wind-induced and other cur- 

 rents in shaping coral reefs ? 



5. What effect have glaciation and deglaciation had on the 

 development of living coral reefs ? 



Before considering the fossil and living coral reefs of the West 

 Indies in their bearing on the answers to these questions, some of 

 the more important criteria to be used in answering the questions 

 wiU be briefly outlined. 



CRITERIA FOR RECOGNIZING SHIFT IN THE POSITION OF STRAND LINE.'J! l^ 



The criteria for recognizing elevation of a former strand line 

 comprise: (a) Coastal terraces bordered inland by escarpments or 

 cliffs that may be inferred to owe their origin to wave cutting; 

 (&) wave-cut grooves in cliffs and sea caves that stand too high to 

 have been formed at present sea level; (c) elevated beaches or bars, 

 which under proper conditions form on shallow marme terraces and 

 at the mouths of embayments; (d) the presence above sea level of 

 organisms that must have lived in the ocean. 



The criteria for recognizing submergence of former strand lines 

 comprise: (a) Indentation of the coast line caused by the sea invad- 

 ing the lower parts of subaerially eroded valleys, the channels of 

 which in many instances are preserved below sea level across and 

 beyond the existing strand line; (b) the presence below sea level of 



