NIAU. 65 



Coming upon Niau from the westward, two low terraces are plainly 

 marked at the northeastern point of the island (PI. 33). As we ap- 

 proached Niau, we could see along the beach spurs or buttresses of the 

 old ledge projecting out from the sand beach, extending at right angles across 

 the shore edge of the reef flat. The lagoon is absolutely closed to the 

 access of the sea, except as it percolates through caverns and fissures of the 

 land rim. It is about three and a half miles across, and it is from 12 to 18 

 feet deep. The slope from the edge of the lagoon is very gradual. There 

 are large mullet living in it, and the shores of the lagoon are Covered with 

 the dead shells of small marine bivalves and gasteropods, which, as was 

 the case in the lagoon of San Salvador, were diminutive examples of larger 

 marine species occurring on the reef Hat. The land rim separating the sea 

 from the lagoon (or sink) is fully 25 feet high, and perhaps half a mile wide. 

 The inner slope of the land rim dips slightly towards the sink. It is com- 

 posed of the same old ledge rock which crops out all around the island, and 

 can be seen forming the outer wall composed of rounded buttresses, more or 

 le.ss widely separated (PI. 33) by reaches of coral sand, forming small beaches 

 composed of material varying from fine coral sand to coarse coral shingle. 

 The beach of the sea face is quite wide, fully 40 to 50 yards. It rises steeply 

 from the inner edge of the reef flat, wliich has been dug out and planed off 

 to low-water mark from the first terrace of the old ledge (Pis. 33 ; 34, fig. 2). 

 The sea rim of the reef platform is slightly raised, Nullipores and Pocillipores 

 growing luxuriantly on it, with deep fissures extending far into the platform 

 from one to twenty feet in width and from a few inches to three fathoms 

 in depth (PI. 34, fig. 2). Many of these fissures form small inlets for boats 

 and canoes, which the natives are quick to make use of in landing and 

 reaching the diminutive lagoon flat inside of the fringing reef rim of the 

 reef platform. 



Pocillipores, Porites, Astrasans, Millepores, Madrepores, and Pavonia grow 

 in abundance from the edge of the reef platform, taking their greatest de- 

 velopment in from three to seven fathoms. None of the corals are large, 

 the heads are small ; and at 20 fathoms, about 100 yards from the outer 

 rim of the platform, there are no living corals ; nothing but coral sand is 

 found, with here and there a patch of corals in slightly shallower water. 



