64 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



Salvador, and on the lagoon shores of Maraki, all of which would supply a 

 mass of small shells as fossils in fine calcareous mud, as characteristic of 

 the interior of lagoon deposits, with here and there corals, or, finally, a mass 

 of corals in the larger lagoons to which the sea has full access. 



As I have already suggested, I am inclined to look upon the basin of 

 Makatea not as the remnant of the lagoon of an elevated atoll, but as a 

 sink produced by atmospheric agencies acting for a long period upon a 

 comparatively flat plateau of elevated coralliferous limestone. The deepest 

 part of the sink may have been formed as a sound when the third terrace 

 was broken through and the sea cut across towards the north end, leaving that 

 remnant to attest the elevation taking place at the time of formation of the 

 third terrace. Similarly the limestone islands at Fiji are often eaten away 

 at the lowest terrace, leaving fragments of higher terraces untouched, which 

 can be seen in some of the higher islands of many lagoons. 



The elevation of the Makatea plateau has taken place too rapidly to allow 

 a connection to be formed between the central sink of disintegration and the 

 deep cuts made by the sea on the flanks of the island, — cuts like those 

 which form the diminutive valleys and crevasses which extend towards the 

 centre of Niue at right angles to the beach line. The elevated plateaus of 

 such islands as Tongatabu, Vavau, Eua, Niue, and Makatea, which are fur- 

 rowed by valleys, or sinks, or areas of drainage, are in marked contrast to 

 such atolls as Pulanga, Ongea, Yangasa, and others in Fiji, — atolls which 

 must at one time have been similar elevated plateaus into which the sea has 

 eaten channels which, communicating with the central sink, very soon eroded 

 the central part of the mass to form sounds or lagoons. 



Niau. 



Plates 33-36, Wl, W2. 



The island of Niau is the only one of the larger atolls of the Paumotus 

 in which there is no entrance into the lagoon, which is merely a shallow 

 salt-water pond. The atoll is nearly circular, about four miles in diameter; 

 its land rim is well wooded. 



