Sect. I. 
KEELING ATOLL. 
23 
reef, was evident from the conglomerate having been 
worn into a point projecting from the beach in a simi- 
larly oblique manner. This retreat in the line of 
action of the breakers may have resulted, either from 
the surface of the reef in front of the islets having 
formerly been submerged, and afterwards having been 
raised by accumulated fragments, or from the mounds 
of coral on the margin having grown outwards. That 
an outward growth of this part is in process, can 
hardly he doubted from the existence of the mounds 
of Porites with their summits apparently lately killed, 
and their sides only three or four inches lower down 
thickened by a fresh layer of living coral. But there 
is a difficulty in this supposition which I must not 
pass over. If the whole, or a large part of the ‘ flat,’ 
had been formed by the outward growth of the margin, 
each successive margin would naturally have been 
coated by the Nulliporse, and so much of the surface 
would have been of equal height with the existing zone 
of living Nulliporse : this is not the case, as may be 
seen in the wood-cut. It is, however, evident from 
the abraded state of the ‘ flat,’ with its original ine- 
qualities filled up, that its surface has been much 
modified ; and it is possible that the inner portions of 
the zone of Nulliporse, perishing as the reef grows out- 
wards, might he worn down by the surf. If this has 
not taken place, the reef can in no part have increased 
outwards in breadth since its formation, or at least 
since the Nulliporse formed the convex mound on its 
margin : for the zone thus formed, which stands 
