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.[81] 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 diagram. 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 for night-shelter by those exploring the range. The lowest, 1,500 feet above the sea, is the Taloko Cave (na-ngara-taloko). The highest is the Ndromo Cave,[82] 2,100 feet, known to the natives as “na-ngara-vatu-ni-ndromo.” Like most of the caves all over the island they occur at the junction of the agglomerates and tuffs, and are to be attributed to the more rapid weathering of the underlying tuffs.... In describing the results of my examination of this mountain-ridge, I will deal in succession with the tuffs, the agglomerates, the junction between these two deposits, and the axis or core of basic rocks.