112 DEPTH AT WHICH Ch. IV. 



depths ranging from 50 to 960 fathoms, and that the 

 bottom always consisted of coral sand. 1 



With regard to the coral-reefs in the Eed Sea, 

 Ehrenberg has the following passage. ' The living 

 corals do not descend there into great depths. On the 

 edges of islets and near reefs, where the depth was 

 small, very many lived ; but we found no more even at 

 six fathoms. The pearlfishers at Yemen and Massaua 

 asserted that there was no coral near the pearl-banks at 

 nine fathoms depth, but only sand. We were not able 

 to institute any more special researches.' 2 I am, how- 

 ever, assured both by Captain Moresby and Lieut. Well- 

 stead, that in the more northern parts of the Eed Sea, 

 there are extensive beds of living coral at a depth of 25 

 fathoms, in which the anchors of their vessels were 

 frequently entangled. Captain Moresby attributes the 

 less depth at which the corals are able to live in the 

 places mentioned by Ehrenberg, to the greater quantity 

 of sediment there ; the situations, where they were 

 flourishing at the depth of 25 fathoms, were protected, 

 and the water was extraordinarily limpid. On the 

 leeward side of Mauritius, where I found the coral 

 growing at a somewhat greater depth than at Keeling 

 atoll, the sea, owing apparently to its tranquil state, 

 was likewise very clear. Within the lagoons of some 

 of the Marshall atolls, where the water can be but little 

 agitated, there are, according to Kotzebue, living beds 

 of coral in 25 fathoms. From these several facts, and 



1 Voyage Bound the World, 1843, p. 379, vol. i. 



2 Ehrenberg iiber die Natur, &c. p. 50. 



