216 



ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



constantly growing Nullipores of tlie outer rim. Towards the ba.se of the 

 coral shingle beach, occasional buttresses of coral breccia rise to a heiu-ht 

 of two to three feet or more, outliers showing the former height of the 

 elevated reef platform. The beach itself is formed of fragments of coral 

 breccia and of recent corals, thrown up on the steep slope of the beach to a 

 height of eight to ten feet above high-water mark, or left as outliers of the 

 disintegration of a former higher reef platform. This coral shingle forms a 

 dam from twenty to seventy feet in width (Pis. 132, fig. 2; 135, fig. 2), on 



PilSITIOX OF THE Bor.E. FrXAFUTI. 



the top of which grows the narrow belt of low vegetation which flanks the 

 cocoanut trees growing towards the lagoon. The inner slope towards the 

 lagoon is much less steep than the outer slope, it is formed of similar frag- 

 ments of coral and of breccia, only of a less size, though occasionally huge 

 boidders have been thrown inland by hurricanes over the upper edge of the 

 shingle dam. or are outliers of the older buttresses. 



The lagoon beach only rises three to four feet above high-water mark ; 

 it consists almost entirely of comminuted coralline foraminiferal sand with 

 little admixture of coral sand which has been laid down on a steep slope 

 towards the lagoon (PI. 132, fig. 1). The coral breccia seen on the outer 



