ON ITS EXTERIOR. VOLCANOES. 383 



islands is both basaltic and trachytic, yet in the point of 

 view now under consideration it is only distinguished by 

 hot-springs in Savu Bay in the island of Vanua Leboo.( 523 ) 

 The Samoa group (Navigator's islands), north-east of 

 the Feejee, and almost due north of the still volcanically 

 active Tonga group, is also basaltic, and is characterised 

 by a great number of linearly arranged craters of erup- 

 tion surrounded by beds of tufa with inbaked pieces of 

 coral. Most remarkable, geologically, is the Peak of 

 Tafua in the island of Upolu belonging to the Samoa 

 group, and not to be confounded with the still burning 

 Peak of Tafoa south of Amargura in the Tonga group. 

 The Peak of Tafua, 2138 feet high, which was first 

 ascended and measured by Dana ( 524 ), has a large crater 

 quite filled with forest trees and crowned by a regularly 

 rounded cone of ashes. There are no traces of lava- 

 streams, but there are scoriaceous lava-fields (Malpais of 

 the Spaniards), with curled and often reticulated surface 

 of the lava, at the conical Mountain of Apia (2576 feet), 

 also in the island of Upolu, as well as at the Peak of 

 Fao which reaches a height of 3000 French (3197 Eng.) 

 feet. The lava-fields of Apia contain narrow subter- 

 rannean caves. 



Tahiti in the middle of the Society islands is much more 

 trachytic than basaltic; it shows, properly speaking, 

 only the ruins of its former volcanic framework ; and 

 amidst these grand remains, forming sometimes lofty 

 walls and sometimes jagged peaks, with vertical preci- 

 pices several thousand feet in depth, it is difficult to 

 decipher the original form of the volcano. Of the two 

 highest summits, Aorai and Orohena, Aorai was ascended 

 first by Dana ( 525 ), and examined by that sound geolo- 



