Sect. III. REEF-BUILDING CORALS LIVE. Ill 



might either invalidate or corroborate this conclusion. 

 Captain Moresby, whose opportunities for observation 

 during his survey of the Maldiva and Chagos Archi- 

 pelagoes were unrivalled, informs me, that 'the upper 

 part or zone of the steep-sided reefs on the inner and 

 outer coasts of the atolls in both groups, invariably 

 consisted of coral, and the lower parts of sand. At 

 7 or 8 fathoms depth, the bottom is formed, as could 

 be seen through the clear water, of great living 

 masses of coral, which at about 10 fathoms generally 

 stand some way, apart from each other, with patches of 

 white sand between them, and at a little greater depth 

 these patches become united into a smooth steep slope 

 Without any coral. Captain Moresby, also, informs me 

 in support of the above statement, that he only found 

 decayed coral on the Padua Bank (northern part of the 

 Laccadive group), which has an average depth of 25 

 to 35 fathoms ; but that on some other banks in the 

 same group, with a depth of only 10 or 12 fathoms, 

 (for instance, the Tillacapeni bank) the coral was 

 living. 



Professor Dana likewise states that during the various 

 and extensive surveys in the Pacific Ocean, made during 

 the United States Exploring Expedition, no evidence 

 was found of corals growing beyond the depth of 20 

 fathoms. 1 I may here add that Sir E. Belcher, though 

 he does not state to what depth living corals extended, 

 says that many soundings were taken off Bow atoll, at 



1 Corals and Coral Islands, 1872, p. 116. 



