176 A NATURALIST IN THE PACIFIC chap, 



gorge of the Satulaki River, which is only elevated about 200 feet 

 above the sea, agglomerates prevailing. In the vicinity of Satu- 

 laki a rather compact basaltic andesite (sp. gr. 2'82) is commonly 

 exposed in position. It is referred to genus 13 of the augite 

 andesites and belongs to the species with felspar-lathes less than 

 •I mm. in average length. It occurs both north and south of this 

 place and in the hill-spurs on either side. This is the bed-rock of 

 the Lambasa plains which here begin and extend to the north 

 coast, being usually covered with submarine tuffs and clays. 



The Thambeyu or Mount Thurston Range 



Mount Thurston is the name given in the Admiralty charts 

 to the highest peak (3,124 feet) of this range. There does not 

 appear to be any general native name. The highest peak visible 

 from the Lambasa side is known as "Thambeyu." The lofty 

 mountain-mass, as it is viewed from Vuinandi, is known as Ulu-i- 

 ndiri-ndiri.^ The whole mountain-range has yet to be properly 

 explored. It is a much more complicated system of mountain- 

 ridges than is indicated in the chart, my acquaintance with it 

 being restricted to the Thambeyu ridge, the elevation of which is 

 2,600 feet above the sea. It trends N.N.W. and S.S.E. ; but its 

 relation to the highest peak of the range could not be ascertained, 

 as we were in the rain-clouds during the two days we were on the 

 mountain. 



I made the ascent from the village of Numbu-ni-a-vula about 

 three miles to the westward, which is only 200 feet above the sea. 

 In the intervening low district a basaltic andesite is exposed in the 

 stream-courses. The structure of the ridge, as indicated by the 

 ascent of its western slope, is shown in the accompanying dia- 

 gram. The core or central axis is formed of massive basic rocks 

 which protrude at the summit and in one or two of the crests 

 of the spurs. The flanks are composed of submarine tuffs and 

 clays overlaid by agglomerates of considerable thickness. The 

 tuffs reach to within 50 feet of the top, whilst the agglomerates 

 extend to within 400 feet of the summit. The results obtained 

 from this ascent are specially interesting, since it afforded me the 

 opportunity of studying in a satisfactory manner the junction of 

 the agglomerates with the tuffs. 



There are two caves on the mountain-side which can be used 



^ Vula Votu is the name of a peak lying to the east. Ngoinangai is a forked 

 mountain still further east. 



