24 
ATOLLS. 
Ch. I. 
between two and three feet above the other parts of 
the reef, is nowhere much above twenty yards in 
width. 
Thus far we have considered facts, which indicate, 
with more or less probability, an increase in the 
diameter of the atoll ; but there are others having an 
opposite tendency. On the S.E. side, Lieut. Sulivan, 
to whose kindness I am indebted for many interesting 
observations, found the conglomerate (D, in wood-cut 
p. 8) projecting on the reef nearly fifty yards in front of 
the islets : we may infer from what we elsewhere see 
that the conglomerate was not originally so much 
exposed, but formed the base of an islet, the front and 
upper part of which has since been swept away. The 
degree to which the conglomerate, round nearly the 
whole atoll, has been scooped, broken up, and the frag- 
ments cast on the beach, is certainly very surprising, 
even on the view that it is the office of occasional gales 
to pile up fragments, and of the daily tides to wear 
them away. On the western side, also, of the atoll, 
where I have described a bed of sand and fragments 
with trees growing out of it, in front of an old beach, 
it struck both Lieut. Sulivan and myself, from the 
manner in which the trees were being washed down, 
that the surf had lately recommenced an attack on this 
line of coast. Appearances indicating a slight eu- 
croaclnnent of the water on the land, are plainer within 
the lagoon : I noticed in several places, both on its 
windward and leeward shores, old cocoa-nut trees 
falling with their roots undermined, and the rotten 
