122 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



lagoon consisted of coral sand, broken shells, Nullipores, corallines, and 

 Foraininifera. 



A sand bar is forming directly across the opening of the passage on 

 the lagoon edge of the inner flat of the atoll. The lagoon flat is nan^ower 

 on the two sides of the passage, but widens out towards the eastern and 

 western beaches of the lagoon, and the widest part of the flat opposite the 

 elitrance is separated from the opening by the deepest part of the lagoon. 



This atoll is well known from a somewhat diagrammatic sketch given by 

 Beechey ; this figure has been reproduced in many text-books, so that it has 

 come to be regarded as the typical atoll. But while it undoubtedly repre- 

 sents an interesting phase in the history of atolls, its constant repro- 

 duction has given it a celebrity out of proportion to its importance, and 

 has gone far to disseminate a very erroneous impression of what an atoll 

 is (PI. 72, figs. 1, 2). 



The atoll can be taken in at a glance from the bridge of a vessel. Its 

 comparatively small size and regular nearly circular outline, its shallow and 

 narrow opening (PI. 72, figs. 1, 2), in addition to its comparatively isolated 

 position rising from an area of great depth, all tend .to emphasize the 

 somewhat exceptional features which characterize it. With Pinaki as a 

 typical atoll, not only was the great irregularity of the many differ- 

 ently shaped' atolls lost sight of, but the composition of the land rim 

 built up of numerous islands, the existence of great stretches of submerged 

 reef, the great depth of many of the atolls, their existence in comparatively 

 shallow areas or position upon great submarine plateaus of very moderate 

 depth, — all these characters were looked upon as constituting essential ex- 

 ceptions to " the atoll " ; " the fairie ring," as typified by Pinaki. On the 

 contrary, it is Pinaki which is an exceptional atoll, and the existence of 

 special conditions readily explains its structure. 



The presence of high dunes on the south face of Nukutavake (PI. 70, fig. 4) 

 and on the east side of Pinaki (PL 72, fig. 3) suggests the possibility of the 

 eventual filling up not only of this lagoon, but also of such islands as Aki- 

 Aki, Tikei, and Nukutavake. Where the central part is more or less dished, 

 as is Aki-Aki and Tike'i, and where, as in Nukutavake especially, the sea 

 face is covered with masses of coral shingle and sand, we have all the 



