298 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



shingle extend far into the belt of hardwood trees which surmounts the 

 high platform of the island. We noticed here, for the first time, a pe- 

 culiar coloration of the water in the gaps or passages leading into the 

 atoll. On the sea face, but more especially on the atoll side of the gap, 

 in from nine to ten fathoms, the color of the water was usually of a 

 metallic blue, and the various colors reflected, as the depth passed into 

 shallower sand bottoms, represented as many hues as those on the 

 feathers of a peacock ; while the main channel itself, sometimes of con- 

 siderable depth, was of a dark blue, rendered only more intense by the 

 contrast of the line of white breakers rolling on the sandy reef flat. 



The wide i-eef flat slopes gradually from the base of the sand or shingle 

 beach ; it consists of recent beach rock or coral shingle conglomerate planed 

 off by the action of the breakers, and is covered with shingle rubble coated 

 by Nullipore growths of variegated colors. Here and there on the outer 

 face of the land rim low sand dunes exist, or they are blown to a consider- 

 able height from the lagoon side, rising sometimes seven to eight feet above 

 the top of the highest part of the shingle beach. This method of encroach- 

 ment by dunes on the land rim from the lagoon side is different from any 

 we have seen in the Paumotu Islands, or other atolls where dunes exist. 

 Usually the widest beaches are on the side of the outer reef platform ; in 

 the case of many of the Marshall Island atolls, coral sand is piled up over 

 extensive flats, on sand bars and sandy islets on the lagoon side. Thus is 

 supplied an immense amount of material blown by the trades sweeping over 

 the lagoon, across to the sea face of the atoll, overwhelming, from the lagoon 

 side, the luxuriant vegetation covering the summit of the narrow land rim. 

 The knolls forming the Nullipore rim of the outer edge of the reef platform 

 are usually highly colored, and in some parts of Kwajalong the outer rim 

 has been deeply indented, forming wide boat passages leading towards the 

 beach slope. In other parts of the reef flat the Nullipore edge forms a wall 

 of considerable height, three to four feet sometimes above high-water mark, 

 as on Enniilabegan Island. As I have stated, the sea face of all the islands 

 is comparatively high, the slope towards the lagoon is gradual ; the green 

 vegetation of the land rim is in striking contrast with the outer black 

 shingle beach, and with the glistening white coral sand reaches. 



