42 ■ "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



A low coral sand beach is tlirown up across the lagoon side of the second 

 channel ; this only stops access of the water at half tide, .and forms a series 

 of shallow pools which run across the depression for a distance of perhaps 

 1000 feet fi-oni the lagoon side towards the sea face (as in PI. 9, fig- !)• 

 The pools open into the lagoon through narrow channels. The central part 

 of the depression also exposes, as in the case of the first cut, the old reef 

 rock ledge, and it is topped with recent beach rock and conglomerate 

 and worn fragments of recent corals and of pieces of the old ledge. 

 The sea face of the cut is quite narrow, passing between the extremities 

 of a steep coral sand and shingle beach which will shortly connect across 

 this narrow channel and completely block access of the sea into the cut. 

 The same thing will in its turn take place across the lagoon end of the cut 

 (PI. 9, fig. 2), so that when access of the sea is completely shut off both on 

 the lagoon and sea face there will remain in the cut near the centre of the 

 island only a shallow pond, which will in its turn be gradually filled with 

 sand blowing over the high beaches from the inner and outer faces, and 

 eventually form a part of the island, to be little by little covered by the 

 vegetation usually found on reef islets. In this manner many of the sinks 

 of the Paumotus have been formed. At the second cut the reef flat plat- 

 form, viz., the old ledge platform, is fully 250 feet wide, and has been 

 planed off, as it were, having a slight rise towards the base of the sand- 

 beach. The rollers lose much of their force comina: in over the outer 

 edge of this ])latform, which is slightly raised and falls off rapidly into deep 

 water. 



The third cut was partially closed both on the lagoon and sea faces, 

 leaving but little access to the water except towards high tide. The 

 shingle across the passage was as high as the shingle on either side of the 

 passage. 



The fifth cut is shut off on both faces, on the lagoon side, by a coral 

 shingle bank of about four feet in height, with a brackish pond near the 

 lagoon side of the island. In the cut parts of the old ledge were exposed, 

 and like the others it was cut through a superstructure of recent beach 

 rock and conglomerate and masses of recent corals and fragments of old 

 ledge. The passage was about 30 to 40 yards wide. On the sea face the 



