32 EXPEDITIOX OF THE "ALBATROSS," 1899-1900. 



To the westward of the Tonga Islands a line of volcanic islands 

 extends nearly 200 miles, from Ilonga Ilapai to Fanna lai, some of 

 which have been active very recently. Falcon Island disappeared in 

 1898, and Lette is still active. Tliis line of volcanoes runs at a distance 

 of from fifteen to twenty miles parallel with the trend of the four 

 irregular]}' shaped plateaux upon which rise the Tonga Islands. They 

 are the summits of a great ridge, over 200 miles in length, sloping very 

 gradually to the westward into deep water, and being somewhat steeper 

 to the eastward, towards the smaller platforms from which rise the 

 volcanic peaks of the group. The plateaux of Tongatabu, Nomuka, 

 Haapai, and Vavau, are separated by deep valleys connecting the eastern 

 and western flanks of the ridge. These four plateaux rise abruptly from 

 the 100-fathom line. The extremity of the southern one is occupied by 

 Tongatabu Island. The land behind the cliffs of its southern coast 

 rises to a height of over 250 feet, and slopes northward very gradually 

 to form the low land which occupies the northern coast of the island, 

 and is, except at Mount Zion and Cook Hill, not more than from five 

 to twenty feet above the level of the sea. At Cook Point and along 

 the southern coast three terraces are indicated. The northern coast is 

 deeply indented by shallow bays, full of islands, reef flats, and reef 

 patches, on which corals grow in great profusion. For a distance of 

 nearly ten miles northward of Nukualofa the plateau is nowhere more 

 than fifteen fathoms deep; and a long tongue runs northward, gradually 

 deepening into twenty to fifty fiithoms to the 100-fathom line. 



The Tongatabu plateau is separated from the Nomuka Group plateau 

 by a fimnel-shaped channel with a depth passing rapidly into 300 

 fathoms from the 100-fathom line. The Nomuka plateau is rectangular. 

 The principal island is Nomuka, where we anchored. We found the 

 island to be composed of Tertiary elevated coralliferous limestone, with 

 a shallow sink, filled with brackish water, occupying the southeastern 

 part of the island. The sink is separated by a high sand-beach, about 

 200 yards wide, from the sea. 



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

 southern extremity, of stratified volcanic material, resembling somewhat 



