126 -ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



line of coral shingle and by a mass of coral boulders and of beach rock 

 (PI. 77, figs. 1-8). The old ledge whicli forms the substratum of the reef 

 platform crops out occasionally, coming up through the movable material 

 covering it in part (PI. 77, fig. 2). On the reef flat rim also numerous bars 

 of shingle and of beach rock form the lagoon edge of the flat (PI. 76, 

 fig. 1); an islet, covered with the same vegetation as that of the two 

 principal islands, built up of sand derived from the interior of the lagoon, 

 extends across the whole width of the reef flat. Two bare sand bars have 

 also been tlirown up on the lagoon side of the reef flat. This islet and the 

 two sand bars are the flrst indications of future islands to be built up on 

 the land rim and to reduce gradually the great open gap of the submerged 

 reef flat which now occupies the southwestern face of the atoll (PL 77, 

 figs. 2, 3). 



Nowhere were we so much struck with the beautiful coloring of the waters 

 of the atolls as in these southern groups, and it baffles description to give an 

 idea of the contrast of colors between the green line of vegetation, the 

 yellow or gray shingle, the cream-colored sand beach, with its wide yellowish 

 brown reef flat banded or dotted at low tide with dark brown masses of 

 ^beach rock, edged with its many-colored knolls of Nullipores or Pocillipores. 

 We then pass through all the shades of light green water to darker green, 

 greenish blue, or dark blue, which a long line of white breakers separates 

 from the darker blue of the deep water on the sea slope. If one were 

 placed high enough to look into the lagoon and take in the whole at a 

 glance, one would see the most wonderful gradations of coloring, passing 

 from the dark blue of the deeper parts of the lagoon to the shallower parts 

 of a lighter hue, next to the greenish blue of the outer edge of the lagoon 

 flat, and finally to the greenish, the greenish yellow, or the lightest imaginable 

 emerald of the shore flats, with here and there a dark blue patch witli metallic 

 reflections skirting a projecting sandy point, where all the imaginable varia- 

 tions of green and blue seem to have blended in the brilliant sunlight re- 

 flected fi'om the placid, hardly rufiled water of the lagoon, or sparkle on 

 the broken sea and swell of the adjoining ocean. In some of the shallower 

 gaps, tlie water after a heavy blow sometimes becomes somewhat muddy 

 and slaty-colored from the amount of silt held in suspension, and the sea 



