92 CORAL-REEFS. 



difference, according to Captain Moresby, 1 between the 

 great branching corals of the Red Sea, and those on the 

 reefs of the Maldiva atolls. 



These facts, which in themselves are deserving of notice, 

 bear, perhaps, not very remotely, on a remarkable circum- 

 stance which has been pointed out to me by Capt. Moresby, 

 namely, that with very few exceptions, none of the coral- 

 knolls within the lagoons of Peros Banhos, Diego Garcia, 

 and the Great Chagos Bank (all situated in the Chagos 

 group), rise to the surface of the water ; w T hereas all those, 

 with equally few exceptions, within Solomon and Egmont 

 atolls in the same group, and likewise within the large 

 southern Maldiva atolls, reach the surface. I make these 

 statements, after having examined the charts of each atoll. 

 In the lagoon of Peros Banhos, which is nearly twenty 

 miles across, there is only one single reef which rises to the 

 surface ; in Diego Garcia there are seven, but several of 

 these lie close to the margin of the lagoon, and need 

 scarcely have been reckoned : in the Great Chagos Bank 

 there is not one. On the other hand, in the lagoons of 

 some of the great southern Maldiva atolls, although thickly 

 studded with reefs, every one without exception rises to the 

 surface ; and on an average there are less than two sub- 

 merged reefs in each atoll ; in the northern atolls, however, 

 the submerged lagoon-reefs are not quite so rare. The 

 submerged reefs in the Chagos atolls generally have from 

 one to seven fathoms water on them, but some have from 

 seven to ten. Most of them are small, with very steep sides ; 2 



1 Capt. Moresby on the Northern Maldiva atolls, Geograph. Journ.> 

 vol. v. p. 401. 



2 Some of these statements were not communicated to me verbally 

 by Capt. Moresby, but are taken from the MS. account before alluded 

 to, of the Chagos group. 



