PRELIMINARY REPORT. 23 
the Fijis we have seen the submarine erosion continue until there is little 
left of many of the atolls beyond the merest islet or rock to indicate its 
structure. In the Paumotus, in the great atolls, which are perhaps only 
the exposed summits of parts of ridges or spurs of an extensive Tertiary 
coralliferous limestone bed, the land-rim of the atoll is, after having been 
denuded to the level of the sea, again built up from the material of its two 
faces, which is thrown up on the wide reef-flats both from the sea face and 
from the lagoon side. We do not find in the Fijis, as in the Paumotus, the 
wide reef-shelves which supply such masses of material from the breaking 
up of the outer and inner edges of the Tertiary limestone platforms, in addi- 
tion to the fragments of the recent corals growing upon the flats and their 
slopes, which, when dead, are thrown up on the top of the reef flats and 
formed into shingle and sand to form a pudding-stone, or a conglomerate, 
or breccia, with the fragments of the old ledge. 
This pudding-stone, or beach rock, is found on all the reef flats of the 
islands of the group. It forms great bars, at right angles usually to the 
shore-line, and upon the sea face of these bars is thrown up coral shingle, 
both old and recent, which builds up short reaches of beaches separated by 
wide flats through which the sea rushes at high-water, or merely covers the 
flats at low tide; while on the lagoon side of the wide reef-flats a similar 
process is going on, throwing up finer sand among the beach-rock bars and 
along their sides, and thus building up little by little, at first small sand- 
bars, then larger bars, or islets, at right angles to the shore-line, and as they 
become larger by accretions from both sides, they finally form islands 
from 1000 to 1200 feet long, according to the width of the reef flat, 
extending from the lagoon edge of the flat to the sea face of the atoll. The 
sand-bars, little by little, become covered with vegetation, and at some 
stages of tide appear like islands and islets situated a considerable distance 
within the lagoon. Whenever the material supplied both from the lagoon 
side and from the sea face is very abundant, the land ring becomes more or 
less solid, the islets become consolidated into islands, separated by narrow or 
wider cuts, until finally they form the larger islands which seem at first 
glance to form a continuous land-rim along the edge of the lagoon, but 
which are often seen to be separated according to local conditions by narrow 
