146 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



throiigli the barrier reefs form the outlets of the waters which accumulate 

 behind the barrier reef flats. 



On the fringing reef platform beyond the Utuofai valley and to the 

 north of it, there are only few corals ; the beach is made up of volcanic 

 sand, occasionally changed to light brown color by a little admixture of 

 coral sand. We then come upon a long, narrow barrier reef flat extending 

 quite unbroken to Boudeuse Pass ; on this flat are scattered numerous 

 negro-heads. 



The first and second islets thrown up on the edge of the barrier reef flat 

 north of Boudeuse Pass are made up of coral sand and coral shingle on the 

 top of the beach (PI. 86, fig. 1) ; inside of the reef extend a number of 

 ledges which are overgrown with coral. The vegetation of these islands is 

 made up of the usual outer belt of shrubs and bushes with an occasional 

 cocoanut tree. Nansouty, the last island on the outer horn of the reef 

 flat, is much larger ; it is covered in part by large trees, similar to those of 

 the main island. Both to the north and south many coral boulders and 

 negro-heads are thrown up on the inner side of the barrier flat. On the 

 wide stretch of the coast south of Artemise Bank there are, again, but few 

 corals ; the beaches are composed alternately of volcanic sand and volcanic 

 sand mixed with coral sand, or of coral sand or coral shingle. 



To the east of Point Venus there is no well-defined barrier reef on the 

 outer edge of the shore platforms, the slopes of the mountains are steeper, 

 and adjoining valleys are separated by knife-edge ridges, which broaden 

 out somewhat fan-shaped as they reach out towards the shore or shore 

 plain, as far south as Mahaena Pass and Nansouty Island. 



Brander's Island is of volcanic structure (PI. 209), and the beach of the 

 bay east of Point Venus is made up of volcanic sand, showing that the 

 wide platform carrying the fringing and barrier reefs of the west side of 

 Tahiti has been formed by submarine erosion. Motu Tehiri and other 

 islands towards Taapuna Pass, enclosed in the fringing reef flat west of 

 Papiete, are volcanic, and the remnants of the volcanic flat platform. We 

 can see the planing down of the cliffs of the coast, at the base of Arue, 

 Haapape and of Tahara promontories, and their extension into the flat of 

 Matavai Bay upon which a few NuUipores and detached masses of corals 



