160 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



Islands is this feature so gi-eatly developed as it is on Bora Bora, where 

 more than two thirds of the outer reef flat is composed of long- islands and 

 islets thickly- wooded, forming a green belt on the barrier reef from one to 

 two miles distant from the base of the steep mountain slopes which rise 

 in the central part of the lagoon (PI. 210, fig. 3). 



Raiatea is separated from Tahaa by a passage about two and a half 

 miles in width (PI. 93, fig. 1), with a greatest depth of twenty-four fathoms. 

 The barrier reef which surrounds the islands of Tahaa and of Raiatea extends 

 directly across the faces of this inlet (PI. 210, fig. 2). Both on the east and 

 west of the passage, and in the centre (PI. 93, fig. 1), several islands and 

 flats indicate the position of former ridges or spurs, which once connected 

 Tahaa with Raiatea, and which have been eroded by the same causes which 

 have cut the submarine plateau extending around the islands, on the outer 

 edge of which the encircling barrier reef is situated. 



It is only around the northern part of Tahaa that the outer edge of the 

 barrier reef fiat is covered with i.slands (Pis. 93, fig. 2 ; 94, figs. 1-3 ; 96, fig. 

 2; 210, fig. 2). To the south of that belt, both on the east and west, the 

 reef is generally awash (PI. 93, fig. 1), or with gaps of from eight to ten feet 

 in depth, separated by patches of coral, the color of the water indicating 

 their presence. In the vicinity of all the ship pa.sses leading into the lagoon, 

 either on the east or the west shore, numerous islands and islets still remain 

 (PI. 93, fig. 3), outliers, indicating the position of the ridges or .spurs of the 

 volcanic slopes which have been eroded, and which once extended to the 

 outer edge of the reef flat (PI. 210, fig. 2), as Mahea and Toahotu Islands at 

 Toahotu Pass on the east side of Tahaa ; we follow these islands along the 

 east shore of Raiatea, as Tetaro and Taoro Islands at Te Avapiti Pass, the 

 islands of Tipaemau and Iriru at Iririi Pass, and similar islands at Teava 

 Moa Pass, at Nao Nao Pass. On the west coast they occur at Toamaro Pass, 

 at Tiano Pass, at Rautoanin, and at Pa'ipa'i. Both on the east and west 

 coasts the islands occnr only at the passes, and the reef flat is indicated by 

 the coral reef patches which we have mentioned. 



The vegetation of the low islands fringing the lagoon is much like that 

 of the Paumotus (Pis. 93, figs. 2, 3 ; 96, fig. 2). Between the islands the 

 sea is pouring into the lagoon, or rushing out according to the stage of the 



