170 "ALBATROSS" TROTICAL PACIFIC EXPEDITION. 



narrow and enclose a shallow lagoon, nowhere more than four fathoms in 

 depth, and thickly stndded with coral knolls. There is an indistinct boat 

 passage leading across the barrier reef flat on the western side of the atoll 

 (PI. 212, fig. 2). To the west of the central part of the island of Aitutaki 

 the barrier reef becomes a fringing reef, the inner part of which is more or 

 less awash, forming an indistinct lagoon. 



The principal island is also connected at its northern extremity with 

 one of the low islands of the belt of islands on the eastern barrier reef flat, 

 at the point where it becomes for a short distance a fringing reef. The 

 island is well wooded, with the exception of the small conical peak on the 

 northern side, which stands out boldly and slopes gradually to the south. 



The plan of Aitutaki (PI. 212, fig. 2) resembles in many ways that of 

 Oeno ' in Fiji, only in the former the principal island is an elevated volcanic 

 island, while in the latter the principal island is low, but both are attached 

 to the outer barrier reef flat and extend far towards the centre of the lagoon. 

 In both, the lagoon is enclosed by a narrow barrier reef flat more or less 

 irregular in outline, somewhat triangular. 



In the southeast corner of the southern barrier reef flat three or four sand 

 keys have been thrown up on an inner extension of the barrier reef flat. The 

 sand islets, like those on the outer belt of the barrier reef flat, will eventually 

 be covered with vegetation. On the beaches of the west face of the principal 

 island mainly volcanic sand is found, and very little coral sand has been 

 thrown up. The islands on the outer barrier reef are in every respect simi- 

 lar to those on the edge of the barrier reef flat of many of the Society Islands. 

 There are a number of volcanic negro-heads on the flats. This group is an 

 excellent example of a volcanic rock flat upon which corals are growing. The 

 formation of the underlying base can be traced, as volcanic outliers crop out 

 at many jjoints on the barrier reef. Aitutaki shows, perhaps as plainly as 

 any other volcanic island we have visited, the manner in which the lagoon and 

 barrier reef flats have been formed from the denudation and erosion of the 

 volcanic mass which once occupied the area indicated by the outer edge of 

 the barrier reef. 



» A. Chart 1176. 



