138 



ALHATROSS" TROPICAL PACIFIC EXPEDITION. 



coral sand islands and islets have been thrown up on the outer faces of the 

 reef flats. 



The fringing and barrier reefs which surround a large island like Tahiti, 

 having a diameter of over thirty miles, and summits reaching a height of 

 more than 7300 feet, appear narrow and unimportant when compared suc- 

 cessively to the barrier reefs and reef flats fringing much smaller islands, 

 as Murea, Raiatea, Huaheine, Bora Bora, and Maupiti, which respectively 

 attain heights of about 4000, 3400, 2300, 2200, and 800 feet. 



It is but a step from such an island as Maupiti, where the central island 

 is reduced to a height of 800 feet to islands like Motu Iti and Tetiaroa, 

 where the central volcanic nucleus has entirely disappeared, and is repre- 

 sented by the flat of volcanic rocks which probably underlies the platform 

 upon which the coral sand islands and islets of these groups have been 



thrown up. It is interesting 

 to note that in Maupiti the 

 southern and western reef 

 flats are covered with masses 

 of volcanic rocks, the outliers 

 of former volcanic islets and 

 islands once occupying the 

 outer rim of Maupiti. 



In the Atlas of the " Voy- 

 age de la Coquille " we find 

 an excellent view of the 

 peaks of Bora Bora (PI. 16) 

 taken from the laa-oon at 



o 



about the place where we 

 anchored off Vaitape. On 

 Plate 17 is given a panoramic view of the islets on the reef flats of the 

 northern face of the island, with Raiatea in the distance. This view 

 is taken from the summit of Pahia which Lesson ascended ; it has been 

 copied by Darwin on p. 3 of the " Structure and Distribution of Coral 

 Reefs." On Plate IS an excellent view of Maupiti from inside the lagoon 



Summits ok Hora Bora. 



