ANNOTATIONS AND ADDITIONS. 67 



in corals, and on the other side in the three long- 

 extended groups or series of Atolls of the Laccadives, 

 the Maldives, and Chagos. The latter series, called 

 by navigators the Chagos-bank, forms a lagoon encircled 

 by a narrow and already much broken, and in great 

 measure submerged, coral reef. The longer and shorter 

 diameters of this lagoon, or its length and breadth, are 

 respectively 90 and 70 geographical miles. Whilst the 

 enclosed lagoon is only from seventeen to forty fathoms 

 deep, the depth of water at a small distance from the outer 

 margin of the coral, (which appears to be gradually sinking), 

 is such, that at half a mile no bottom was found in sounding 

 with a line of 190 fathoms, and, at a somewhat greater 

 distance, none with 210 fathoms. (Darwin, Structure of 

 Coral Reefs, p. 39, 111, and 183.) At the coral lagoon 

 called Keeling- Atoll, Captain Fitz-ftoy, at a distance of only 

 two thousand yards from the reef, found no soundings 

 with 1200 fathoms. 



" The corals which, in the Eed Sea, form thick wall-like 

 masses, are species of Meandrina, Astrsea, Eavia, Madrepora 

 (Porites),Pocillopora (hemprichii),Millepora, andHeteropora. 

 The latter are among the most massive, although they are 

 somewhat branched. The corals which lie deepest below the 

 surface of the water in this locality, and which, being mag- 

 nified by the refraction of the rays of light, appear to the 

 eye like the domes or cupolas of a cathedral or other large 

 building, belong, so far as we were enabled to judge, to 

 Meandrina and Astrsea." (Ehrenberg, manuscript notices.) 

 It is necessary to distinguish between separate and in part 



