TAHANEA. 85 



fine outcrops of the old ledge, buttresses reaching nearly to the water's edge 

 across the sand beaches, and separated by coral sand beaches or by coral 

 rag shingle beaches (Pis. 52, fig. 1 ; 53, fig. 1). 



To the south of the inner line of islands extends an immense flat covered 

 only with a few feet of water (Pis. 52, fig. 2 ; 53, fig. 3), tlie whole flat shin- 

 ing brightly in the sun as a light green sheet, in contrast to the darker 

 greenish blue band of deeper water extending towards the south. This flat 

 covers so great a proportion of the lagoon that its greenish light, reflected 

 against the clouds, can often be seen long before the atoll itself looms in sight. 

 Other shallow lagoons are also detected in this manner. The greater part of 

 the lagoon is quite shallow, not more than from one to two fathoms in 

 depth. A great many sand bars are found all through the lagoon. 



This atoll is intermediate in structure between such an atoll as 

 Fakarava, which has a comparatively deep lagoon full of islands, and a 

 solid island or an island with an insignificant lagoon or sink, such as Tikei. 



The northwestern part of Anaa will soon be filled with islets ; in that part 

 of the lagoon sand is constantly piling up inside on the lagoon side, and on 

 the sea face reef coral shingle beaches are thrown up (PI. 53, fig. 2). At 

 a distance the bight where the boat pass is situated looks like an inlet 

 to the lagoon between the islands, but the lagoon is shut off by a wide 

 flat, the extension of the reef flat to the east of the secondary lagoon. 



On the east, as well as on the west side of the atoll, are alternating 

 low and high gaps. On the east face the old ledge crops out in a series 

 of high spurs running diagonally across the face of the beach. 



Tahanea. 



Plates 54, 00, 201, P.03. 



Tahanea Island is about twenty-five miles long, it is irregularly elliptical, 

 and perhaps ten miles at its greatest width. On the north .side within a 

 distance of about two miles there are three entrances for small vessels into 

 the lagoon. The land rim on the north side is well wooded, while on 

 the southern face the islands are ffenerallv bare. 



