54 "ALBATEOSS" TROPICAL PACIFIC EXPEDITIOX. 



are on the north side. This may be due to the fact that the land belts 

 of the former atolls ai'e rapidly building up from the lagoon side, the 

 tendency of the prevailing winds being to keep an opening clear on the 

 western faces. 



Matahiva. 



Plates 20, fig. 1 ; 201, 202 ; 204, fig- 4- 



Matahiva, as seen about four miles o£E from the southeast, appears 

 well wooded, with cocoanut patches and an outer belt of vegetation of the 

 usual type characteristic of the Paumotu atolls. We could see traces of 

 the old ledge cropping out here and there, separated by sand reaches 

 which seem to have overwhelmed the ledge. There appear to be very 

 few large breaks on the eastern face of the island. I was informed by the 

 gendarme at Rangiroa, and by Mr. Edward Bonnefin, a former resident 

 of Matahiva, and now of Makatea, that the lagoon of this atoll is very 

 shallow, full of ledges and islets, and that one can get about in the 

 lagoon only in a flat boat. From what we could see steaming around 

 the island it is evident that the passes and cuts once separating the 

 islands and islets, similar to the single opening now left, through which 

 boats enter the lagoon (PI. 20, fig. 1), have been, as in other atolls of 

 the group, gradually closed by the sand blown along the inner shore of 

 the lagoon derived from the breaking up of the ledges of the interior ; 

 the sand blowing on the lagoon side of the outer edge of what is left 

 of the ledge, and gradually overwhelming it, the rapidity of this woi-k 

 depending upon the amount of ledge rock exposed to the action of the 

 wind and sea inside of the lagoon. 



As we steamed around Matahiva, the outer " reef platform seemed to 

 be much wider than we had seen it either at Rangiroa or Tikahau ; 

 it varied from 200 to 300 feet in places, judging from the position of 

 the breakers relatively to the shore coral sand beach. 



Between the more or less continuous ridges of the old ledge, running 

 diagonally or at right angles to the beach, wide patches and reaches of sand 

 extend. Fjom the greater width of the shore platform of this the western- 

 most island of the group more material is supplied on the sea face, and thus 



