30 
ATOLLS. 
Cn. I. 
The form of the bottom, as given by Captain 
Beechey in his sections of the atolls in the Low 
Archipelago, exactly coincides with that already de- 
scribed in Keeling atoll : it gradually slopes to about 
twenty fathoms, at the distance of between one and 
two hundred yards from the edge of the reef, and 
then plunges at an angle of 45° into unfathomable 
depths. 1 The nature, however, of the bottom seems 
to differ, for this officer 2 informs me that all the 
soundings, even the deepest, were on coral, but he 
does not know whether dead or alive. The slope 
round Christmas atoll (Lat. 1°4' N., 157° 45' W.), de- 
scribed by Cook, 3 is considerably less ; at about half a 
mile from the edge of the reef, the average depth was 
about fourteen fathoms on a fine sandy bottom, and at 
a mile, only between twenty and forty fathoms. It has 
no doubt been owing to this gentle slope, that the strip 
of land surrounding its lagoon, has increased in one 
part to the extraordinary width of three miles ; it is 
formed of successive ridges of broken shells and corals, 
like those on the beach. I know of no other instance 
of such width in the reef of an atoll ; but Mr. F. D. 
1 The slope of the bottom round the Marshall atolls in the 
Northern Pacific is probably similar : Kotzebue (First Voyage, vol. ii. 
p. 16) says, ‘ We had at a small distance from the reef, forty fathoms 
depth, which increased a little further so much that we could find no 
bottom.’ 
2 I must be permitted to express my obligation to Captain Beechey, 
for the very kind manner in which he has given me information on 
several points, and to own the great assistance I have derived from 
his excellent published work. 
3 Cook’s Third Voyage, vol. ii. chap. 10. 
