44 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



rock thrown upon the shore platform, many of them of great size (PL 11). 

 Two masses were measured, one 18 feet long by 5 wide, and varying in 

 height from 6 to 7 feet; another nearly cubical mas.s measuring 9 feet. 

 These masses are detached during storms or by high seas from the sea face 

 of the old reef ledge and hurled towards the shore, where they are gradually 

 broken up into smaller masses (Pis. 8; 12, fig. 2), and eventually ground 

 into the high coral shingle (Pis. 5 ; 12, fig. 1) and sand beaches of the sea 

 face ; or are outliers of the old ledge platform. 



The old reef rock ledge exposed in the cuts (PI. 9, fig. 1) can be traced 

 all the way across the land rim till it merges into the old ledge of the sea 

 face flat (PI. 8, fig. 2), and with its extension on the lagoon side, which can 

 be traced reaching into two to three fathoms. On the lagoon side similar 

 mas.ses, but smaller (PI. 9, fig. 2), have also been thrown up after being de- 

 tached from the outer edge of the lagoon platform, or they are left as on 

 the sea face standing as remnants still connected with the ledge of the old 

 reef rock of tertiary coralliferous limestone. Some of these ancient masses 

 projected in the bushes beyond the line of vegetation. It was of course not 

 always possible to determine whether they were parts of the old ledge or 

 loose boulders more or less covered by the surrounding fragments of loose 

 corals. When below low-water mark their connection with the old ledge 

 was concealed by the mass of beach rock and fragments of conglomerate 

 surrounding the lower parts. 



Nui Nui Island, off the lagoon entrance of Tiputa Pass, is, like Mohican 

 Island, composed of ancient reef rock ; the extremities are being gradually 

 cut up into masses and smaller boulders, and finally spread out into the 

 coarse sand flat. The destruction of the islands and islets off the lagoon 

 side of Tiputa and Avatoru Passes (Pis. 7 ; 12, fig. 1) shows plainly how 

 much material has been removed from the inner ledges of the lagoon, gradually 

 reducing them to the water's edge, and finally, by the action of the waves 

 and currents, as well as the solvent action of the sea, gouging out the 

 inequalities of the lagoon, deepening it little by little, — agencies which 

 have been at work steadily since the last period of elevation of the tertiary 

 coralliferous limestones, when the area of the exposed limestones was not 

 only far greater than it is at the present time, but when the land probably 



