Sect. II. ATOLLS. 31 



able, as the slope is generally less abrupt in front of 

 channels through a reef, owing to the accumulation of 

 sediment. At Egmont Island, also, at 150 fathoms 

 from the reef, soundings were struck with 150 fathoms. 

 Lastly, at Cardoo atoll, only sixty yards from the reef, 

 no bottom was obtained, as I am informed by Captain 

 Moresby, with a line of two hundred fathoms ! The 

 currents run with great force round these atolls, and 

 where they are strongest, the inclination appears to be 

 most abrupt. I am informed by the same authority, 

 that wherever soundings were obtained off these 

 islands, the bottom was invariably sandy : nor was there 

 any reason to suspect the existence of submarine cliffs, 

 as there was at Keeling Island. 1 Here then occurs a 

 difficulty ; — can sand accumulate on a slope, which, in 

 some cases, appears to exceed fifty-five degrees ? It 

 must be observed, that I speak of slopes where sound- 

 ings were obtained, and not of such cases, as that of 

 Cardoo, where the nature of the bottom is unknown, 

 and where its inclination must be nearly vertical. M. 

 Elie de Beaumont 2 has argued, and there is no higher 

 authority on this subject, from the inclination at which 

 snow slides down in avalanches, that a bed of sand or 



1 Off some of the atolls in the Low Archipelago the bottom appears 

 to descend by ledges. Off Elizabeth Island, which consists of raised 

 coral-rock, Capt. Beechey (p. 45, quarto ed.) describes three ledges : the 

 first slopes gently from the beach to a distance of about fifty yards ; 

 the second extends two hundred yards with a depth of twenty-five 

 fathoms, and then ends abruptly, like the first; and immediately 

 beyond this there is no bottom with two hundred fathoms. 



2 Memoires pour servir a une description Greolog. de France, tome 

 iv. p. 216. 



