22 
ATOLLS. 
Cn. I. 
tion of the whole atoll, I was at first unable to imagine 
what cause could have killed so large a field of coral. 
Upon reflection, however, it appeared to me that the 
closing up of the above mentioned channels would be 
a sufficient cause ; for before this, a strong breeze 
by forcing water through them into the head of the 
lagoon, w r ould tend to raise its level. But now this 
cannot happen, and the inhabitants observe that the 
tide rises to a less height, during a high S.E. wind, at 
the head than at the mouth of the lagoon. The corals, 
which, under the former condition of things, had at- 
tained the utmost possible limit of upward growth, 
would thus occasionally be exposed for a short time to 
the sun, and be killed. 
Besides the increase of dry land, indicated by the 
foregoing facts, the exterior solid reef appears to have 
grown outwards. On the western side of the atoll, the 
‘ flat ’ lying between the margin of the reef and the 
beach, is very wide : and in front of the regular beach 
with its conglomerate basis, there is, in most parts, a 
bed of sand and loose fragments with trees growing 
out of it, which apparently is not reached even by the 
spray at high water. It is evident some change has 
taken place since the waves formed the inner beach : 
that they formerly beat against it with violence was 
evident, from a remarkably thick and water-worn point 
of conglomerate at one spot, now protected by vegeta- 
tion and a bank of sand ; that they beat against it in 
the same peculiar manner in which the swell from 
windward now obliquely curls round the margin of the 
