32 ATOLLS. Ch. I. 



mud cannot be formed at a greater angle than thirty 

 degrees. Considering the number of soundings on 

 sand, obtained round the Maldiva and Chagos atolls, 

 which appear to indicate a greater angle, and the ex- 

 treme abruptness of the sand-banks in the West Indies 

 as will be mentioned in the Appendix, I must conclude 

 that the adhesive property of wet sand counteracts its 

 gravity, in a much greater ratio than has been allowed 

 for by M. Elie de Beaumont. From the facility with 

 which calcareous sand becomes agglutinated, it is not 

 necessary to suppose that the bed of loose sand is thick. 

 Capt. Beech ey has observed, that the submarine 

 slope is much less at the extremities of the more 

 elongated atolls in the Low Archipelago, than at their 

 sides ; in speaking of Ducie's Island he says l the 

 buttress, as it may be called, which ' has the most 

 powerful enemy (the S.W. swell) to oppose, is carried 

 out much further, and with less abruptness, than the 

 other.' In some cases, the less inclination of a certain 

 part of the external slope, for instance of the northern 

 extremities of the two Keeling atolls, is caused by a 

 prevailing current which there accumulates a bed of 

 sand. Where the water is perfectly tranquil, as within 

 a lagoon, the reefs generally grow up perpendicularly, 

 and sometimes even overhang their bases : on the 

 other hand, on the leeward side of Mauritius, where 

 the water is generally tranquil although not invariably 

 so, the reef is very gently inclined. Hence it appears 



1 Beechey's Voyage, 4to. ed. p. 44. 



