PINAKI. 121 



The gap which is the onl}- opening into the lagoon of Pinaki is about 

 500 yards wide, and tlie land rim at the opening is nearly 1200 feet 

 wide (PI. 72, figs. 2, 3). No water can come into the lagoon except during 

 the last part of the rising tide. The lagoon is filled with numerous islets 

 (Pis. 74, fig. 1 ; 75, fig. 1 ; 206, fig. 3) which rise on the lagoon edge of the 

 inner reef flat, which in places is fully 600 feet wide (PI. 74, fig. 1). Mr. 

 Alexander counted no less than 116 of these islets; they are all topped 

 with dead Tridacna shells, and there are great windrows of these on the 

 edge of the lagoon flat, close to the lagoon beach of the land rim (Pis. 75, 

 fig. 3 ; 206, fig. 3). The Tridacna islets are all small, ten by twelve feet 

 about, not more than tliree feet high, and their slopes are covered with 

 Madrepores. Many of the islets are connected by shallow flats. The living 

 Tridacnas are found in great number in the deeper parts of the lagoon towards 

 the northern end of the atoll, where they occur packed much as oysters in 

 an oyster bed. Besides the Tridacnas, the bottom of the lagoon and stretches 

 of the lagoon flat are covered with a species of Area, the dead shells of which 

 are thrown up in immense masses on the shallow parts of the lagoon and 

 on the inner beaches. On the west end of the island there is in the lagoon 

 a huge bed of these Areas. The lagoon in some places is from three to four 

 fathoms deep below the inlet. The water is abnormally warm, — much 

 above the temperature of the outer sea water. The lagoon contained 

 many fishes. 



The old ledge crops out here and there on the sea face. To the west 

 of the entrance there is a good exposure of it (Pis. 72, figs. 1, 2 ; 206, 

 fig. 3), as well as in the middle of the entrance to the lagoon (Pis. 72, 

 fig. 3 ; 74, fig. 2 ; 75, fig. 2), where an outcrop forming an elongated ledge 

 divides the channel into two passages (PI. 75, fig. 2), while on the sides 

 of the passages of the channel the old ledge is covered by beach rock, 

 recent conglomerate, coral boulders, and shingle, — a condition of things 

 very similar to that which we have observed in the gaps of so many of the 

 Paumotu atolls (Pis. 72, fig. 1; 74, fig. 2; 75, fig. 3). The beach rock 

 cropped out here and there in the interior of the lagoon. The sand which 

 is blown into the lagoon over the land rim is cemented into fine mud when 

 mixed with the mass of decaying Areas and Tridacnas. The bottom of the 



