242 " ALBATROSS " TROPICAL TACIFIC EXPEDITION. 



have formed in the platform lagoons. The bars of nibble on the outside 

 edge of the reef platform are at first covered with a little vegetation, but as 

 they become larger spurs or islets, and extend out into the lagoon, the coat- 

 ing of vegetation increases. Low sand dune reaches, overgrown with veg- 

 etation, unite them on the lagoon side, and form a kind of platform lagoon 

 on the outside edge of the reef flat differing from any we have seen before. 

 The secondary platform lagoons can be looked upon as owing their origin 

 primarily to old gaps, then to dam lagoons, then to lagoon rims filled with 

 islands. On the eastern face a succession of such secondary lagoons exists, 

 showing that the land rim must have been a series of islets like those of 

 Tapeteuea, running perpendicularly to the outer reef flat line. No landing 

 was possible on the east face of Apamama. 



Near the south point on the east side, the reef platform becomes narrower 

 as it extends towards the south, and the low wall of old ledge which flanks 

 that part of the atoll is gradually changed into more or less indistinct but- 

 tresses ; they are situated well above high-water mark, and run diagonally 

 across the steep beach of that part of the land rim. Behind these ledges 

 sand dunes are formed which raise the beaches or the land rim to a greater 

 height than is usual in the Ellice Islands (PI. 139, fig. 3). 



At the southernmost point of Apamama the old ledge reaches well up on 

 the beach and has been elevated at least seven to eight feet. This is not 

 beach rock, but is part of the old elevated coralliferous limestone. Beach 

 rock or coral conglomerate is found on the outer edge of the reef flat, or at 

 the base of the beach. A wide coral sand beach separates the old ledge 

 buttresses from the beach rock, or coral conglomerate, or breccia deposited 

 between its outliers ; this, being softer than the old ledge rock, has in great 

 part been washed away. On the south side we found the same formation 

 as on the east face, a series of secondary platform lagoons, gaps, and small 

 bays ; here and there beach rock or coral conglomerate ledges are exposed, 

 the higher parts of which must have been elevated at least three feet above 

 high-water mark. One of the gaps is broad, fairly shallow, and leads 

 from the reef flat into the lagoon. Another bay is. perhaps, larger than 

 any we have seen on the east face ; it is probably older also, the dam between 

 it and the lagoon side being of considerable width ; the two spits flanking it 



