EQUATOEIAL POLYNESIA. 



469 



continuing the igneous system of New Zealand. Here Tofua (2,800 feet) was the 

 scene of an eruption in 1885, and Kao (5,000 feet) has been frequently disturbed 

 during the historic period. Late, west of the Vavao group, emitted flames in 

 1854, and its northern neighbour Fonualai (Amargura) was nearly blown away by 

 a terrific explosion in 1846. Niua, which stands in a line with the volcanic axis, 



Fig. 204.— Tonga-Tabu. 

 Scale 1 : 700,000. 



175° 20' 



West or Greenwich 



174° 50' 



Depths. 



Oto 1,000 

 Fathoms 



] ,000 Fathoms 

 and upwards. 



12 Miles. 



presents a remarkably regular oval shape, with a lake of like form within the 

 circuit of its vast crater. Tonga really comprises two distinct chains, a western 

 with several lofty isolated cones, and an eastern consisting of low islands. Here 

 the large island of Tonga-Tabu itself is merely a level plain of coralline sands un- 

 derlying a thick layer of extremely fertile vegetable humus. The whole island is 

 covered with a rich vegetation of bread-fruit trees, palm-groves, and bananas. 

 Other coralline islands, such as the picturesque Yavao group and Nine farther east 

 have been raised to a certain height above sea-level. 



