THE PAUMOTUS. 21 



the Fijis we have seen the submarine erosion continue until there is little 

 left of many of the atolls bej'ond the merest islet or rock to indicate its 

 stnicture. In the Paumotus, in the great atolls, which are perhaps only 

 the exposed summits of parts of ridges or spurs of an extensive tertiar}- 

 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 

 fiices, 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 suppW such masses of material from the breaking 

 up of the outer and inner edges of the tertiary limestone platfornas, 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 Oats 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 froTn 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 rim becomes more or 

 less solid, the islets become consolidated into islands, separated by narrow or 

 wider cuts, until finallj" 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 



