NUKUTIPIPI. 127 



for quite a distance is discolored and in marked contrast to the usual dark 

 blue color of the ocean. 



There is a wide gap between the two main islands of the lagoon on the 

 northwestern side of the atoll (Pis. 77, fig. 2 ; 206, fig. 4). The small island 

 occupies a part of the northwestern face of the atoll, while the larger island 

 flanks the lagoon on the north and northeast (PI. 77, figs. 2, 4). This and 

 the other atolls of the Duke of Gloucester Islands may indeed be called 

 pocket editions of characteristic Paumotu atolls. In the cut awash the beach 

 rock is in part overlying the old ledge, huge boulders of which are left 

 cropping out from the underlying foundation (PI. 77, fig. 2), and crops out 

 again on the inner face of the atoll. Vegetation covered in part the top 

 of the sea beach as well as that of the lagoon face, and ran partly in 

 between the shrubs and trees, showing that but little sand is as yet blown 

 across the beach into the lagoon. 



The larger island, forming the northerly and easterly side of the atoll, 

 varies greatly in width, from 150 to 300 yards. At the southwest point of 

 the smaller island the coral shingle beach must be fully fifteen feet in height 

 in places, as a general rule at least twelve. On both islands the vegetation 

 comes down below the summit of the inner and outer beaches, which are 

 also well protected by grass extending on the lagoon face of the beach 

 towards the interior of the land rim. The varying width and the narrow 

 points of the land rim indicate probably the position of former gaps, which 

 have gradually closed and connected the separate sand bars, islets, and 

 islands once undoubtedly occupying the area now covered by the large 

 island- 



The reef flat is from 200 to 300 feet wide, and sand bars and incipient 

 islets are forming on the lagoon edge of the reef flat of the land rim. The 

 extent of the reef flat extension into the lagoon is indicated by the . light 

 green water (PI. 206, fig. 4). 



If the extension of the dunes were not kept in check by vegetation, com- 

 paratively small lagoons like those of the Duke of Gloucester Islands, would 

 become filled and closed very rapidly. At present some of them are in 

 equilibrium, new material is added by the corals on the south face where it 

 is now building up sand bars and islets on the reef flat, while before the 



