176 "ALBATROSS" TEOPICAL PACIFIC EXPEDITION. 



Nomuka Iki, the island next to Nomuka, we found to consist, at its south- 

 ern extremity, of stratified volcanic material, resembling somewhat the so- 

 called soap-stone of Fiji. I was informed that other islands in this group, 

 near Tonumeia, in the centre of the Nomuka Plateau, were volcanic. 

 Mango, as we could see it from our anchorage, appeared to be volcanic. So 

 that this part of the Tongas is, as has been indicated by Lister, like the Lau 

 group in Fiji, made up of islands in part volcanic and in part composed of 

 elevated coralliferous limestone or wholly volcanic and wholly limestone. 

 In Fiji the trend of the large volcanic islands and of the Lau group forms 

 an angle, in the Tonga Archipelago, the line of volcanoes and the axis of the 

 Tonga Plateaus are parallel. The eastern edge of the Nomuka Plateau 

 (which we did not visit) is edged with small low islands. We merely 

 steamed by the western islands of the Haapai group, but close enough to 

 see that Tongua, Kotu,^ and Fotuhaa, which vary in height from 120 to 

 200 feet, are composed of elevated limestone. ' The eastern flank of the 

 Haapai Plateau is edged with long, low islands, with extensive coral reefs 

 along the western reef fiats of these islands. 



The Haapai Plateau is triangular (Pis. 217, 218), with isolated islands 

 rising on the northwestern side from the deep water separating it from the 

 Vavau Plateau. It is separated from the Nomuka Plateau by a narrow chan- 

 nel with over 300 fathoms of water. 



The northernmost plateau of the broad ridge of the Tonga Islands is the 

 Vavau Plateau (PI. 219). This is elliptical, with a long tongue extending 

 on the eastern face of the ridge toward the northern point of the Haapai 

 Plateau, ending in isolated banks (the Disney Reef and Falcon Bank), lying 

 to the northward of the broad channel, with over 400 fathoms sepai'ating it 

 from the Haapai group. The Vavau group is by far the most picturesque 

 of the Tonga Islands. It consists of the principal island of Vavau, extend- 

 ing across the northern part of the Vavau Plateau. Several parts of the 

 island of Vavau, as at the southwestern extremity, at the entrance to the 

 harbor of Neiafu, and at Neiafu, are finely terraced ; four terraces are in- 

 dicated there, and other flat-topped smaller islands show traces of two or 



1 Lister considers that the raised rocks which form tlic edge of the sink of the island of Kotu must 

 have surrounded a lagoon, when they stood at the level of the sea. 



