BY H. I. JENSEN. 661 



1886. Four or jive days after the eruption of Tarawera, White 

 Island, in the Bay of Plenty, became unusually active; and two 

 months later there was a violent eruption of Niuafau in the 

 Tongan group. Again, in 1902 there was a violent eruption in 

 the Kermadec Islands, a violent eruption as already described in 

 Savaii, and severe earthquakes at Cheviot, New Zealand, and 

 in Samoa. 



Admission of sea-water. — There can be no doubt that the 

 explosive violence of the youngest volcano in the world in its 

 early stages was due to the admission of sea-water. The evolu- 

 tion of hydrochloric acid (HC1) and the deposition of common salt 

 (NaCl) in the fissures are clear proof that sea-water had found its 

 way down to the hot lavas. 



6-Tongan Geology as beaking on the nature op the outbreak. 



An excellent paper on the " Geology of the Tongan Islands" 

 by Mr. J. J. Lister appeared in the Quarterly Journal of the 

 Geological Society (Vol.xlvii., November 2nd, 1891). Not being- 

 acquainted with this paper until after my return to Sydney, I 

 made some observations in Vavau, Haapai and Tongatabu which 

 I find, though less complete, agree in all respects with Lister's. 



There is, in the Tongan group, a line of volcanic islands, 

 situated to the west of the islands, which are built wholly 

 or partly of coral rock. The volcanic line runs about N. 

 22° E., and, if produced north and south, passes through Samoa, 

 the Kermadec Islands, White Island, and the Taupo zone in New 

 Zealand. The wholly volcanic islands of the Tongan group 

 lying on this line are Pylstaart, Falcon Island, Tofua, Kao, 

 Latte, Amargura, Toku, Boscawen, Keppel Island and Niuafou.* 

 The coralline islands are partly raised atolls, and partly raised 

 reefs. Elevation has usually been greatest on the eastern side, 

 which is, in most cases, the highest. The island of Eua, which 

 lies S.E. of Tongatabu, is by far the highest in the group, 

 exceeding in places 1000 feet. 



* See Map of the Tongan Islands, Admiralty Charts. 



