90 CORALS AND CORAL LSLANDS. 



his survey of the Maldives and Chagos group, found, at seven 

 or eight fathoms, great masses of Hving coral ; at ten fathoms, 

 the same in groups with patches of white sand between ; and, 

 at a litde greater depth, a smooth steep slope without any 

 living coral ; and further, on the Padua Bank, the northern 

 part of the Laccadive group, which had a depth of twenty- 

 five to thirty-five fathoms, he saw only dead coral, while on 

 otlier banks in the same group, ten or twelve fathoms under 

 water, there was growing coral. 



In the Red Sea, however, according to Captain Moresby 

 and Lieutenant Wellstead, there are, to the north, large beds 

 of living corals at a depth of twenty-five fathoms, and the 

 anchors were often entangled by them ; and he attributes this 

 depth, so much greater than reported by Ehrenberg, to the 

 peculiar purity, or freedom from sediment, of the waters at that 

 place. Kotzebue states that in some lagoons of the Marshall 

 group he observed living corals at a depth of twenty-five 

 fathoms, or one hundred and fifty feet. 



Professor Agassiz observes that about the Florida reefs 

 the reef-building corals do not extend below ten fathoms. 

 Mr. L. F. de Pourtales states that he found species of Ocu- 

 lina and Cladocora off the Florida reefs living to a depth of 

 fifteen fathoms. 



It thus appears that all recent investigators since Quoy and 

 Gaymard have agreed in assigning a comparatively small depth 

 to growing corals. The observations on this point, made during 

 the cruise of the Wilkes Explormg Expedition, tend to confirm 

 this opinion. 



The conclusion is borne out by the fact that soundings in 

 the course of the various and extensive surveys afford no evi- 

 dence of growing coral beyond twenty fathoms. Where the 

 depth was fifteen fathoms, coral sand and fragments were 

 almost uniformly reported. Among the Feejee Islands, the 

 extent of coral-reef grounds surveyed was many hundreds of 

 square miles, besides the harbours more carefully examined. 

 The reefs of the Navigator Islands were also sounded out, 

 with others at the Society group, besides numerous coral 



