MAYOR— THE REEFS OF TUTUILA, SAMOA. 235 



markably flat floors, of the bottoms of Pacific lagoons ; whereas such 

 facts are readily understood if we suppose the ocean level to have 

 risen about 20 fathoms since glacial times. An obstacle to the gen- 

 eral acceptance of Daly's theory lies, however, in the fact that if 

 these level-bottomed submerged banks were formed at a time of 

 lowered ocean level caused by the withdrawal of water from the 

 seas to form the polar ice-caps, then the submarine banks of the 

 tropical Pacific should be submerged to the same depth as those of 

 the tropical Atlantic, but over the Bahama Banks we find an area 

 of 27,000 square miles with depths only varying from 2 to 5 fathoms, 

 instead of 15 to 20 fathoms as in the Pacific atoll lagoons. 



On the other hand, the remarkably uniform and relatively nar- 

 row width of considerably less than a mile shown by the atoll rims 

 of the Paumotos, Ellis, Gilbert, and Marshall Islands suggests that 

 these atoll groups are all of about one and the same age, and as we 

 now know the growth-rate of Pacific corals to be almost twice as 

 rapid as that of corresponding genera in the Atlantic it would seem 

 that these atolls could have attained their present stage by growth 

 commenced after the close of the last glacial epoch. The living 

 coral reefs of the Pacific are probably less than 40,000 years old, 

 and this is strongly suggestive of the validity of Daly's theory in so 

 far as it applies to the modern reefs of the Pacific. The growth- 

 rate of Samoan corals is rapid, massive Pontes heads growing up- 

 ward about 18 mm., branched Pontes 30 mm., Pocillopora 38 mm., 

 and Acropora 55 mm., per annum. Thus a reef of massive Pontes 

 might grow upward 100 feet in 1,600 years. It will be recalled that 

 Stanley Gardiner estimated that in the Maldives a coral reef might 

 become 100 feet thick in 1,150 years ; and thus our independent esti- 

 mates are of the same order of magnitude. 



Making use of diving apparatus, I have studied the reefs at 

 depths of 2 to 6 fathoms, and find that when corals die which grew 

 in depths below the influence of the breakers, they commonly remain 

 in place and soon became coated with layers of lithothamnion, and 

 are thus not only preserved as elements of the reef but the stony 

 mass actually increases in volume, the lithothamnion cementing all 

 dead elements of the reef into a more or less compact framework 

 into the interstices of which sand and other fragments soon settle. 



