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 200 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. (Off some of the islands
in the Low Archipelago the bottom appears to descend by ledges. Off
Elizabeth Island, which, however, consists of raised coral, Captain Beechey
(page 45, 4to edition) describes three ledges: the first had an easy slope
from the beach to a distance of about fifty yards: the second extended two
hundred yards with twenty-five fathoms on it, and then ended abruptly, like
the first; and immediately beyond this there was no bottom with two hundred
fathoms.) 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 soundings 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
("Memoires pour servir a une description Geolog. de France," tome iv., page
216.) 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 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 appears to indicate a greater angle, and the extreme
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