XII THE AVUKA RANGE 



179 



coloured marl-like rock, a centimetre thick, which is formed of 

 the same materials but in a clayey condition. Beneath this is the 

 calcareous foraminiferous palagonite-tuff referred to in the first 

 paragraph. 



It is apparent that for some time before the agglomerates 

 began to accumulate on the sea-bottom there had been a fairly 

 uniform deposit of submarine tuffs, evidently in rather deep water. 

 Then followed a period during which the finest mud was deposited 

 which is represented by the thin layer of chocolate-coloured clay. 

 This was succeeded by the deposition of coarser sedimentary tuffs 

 forming a layer about an inch in thickness. Then commenced 

 the accumulation of the agglomerates, of which the materials 

 were at first small and afterwards larger in size. 



(4) The core or axis of volcanic rocks. — This is represented on 

 the summit by masses, 2 to S feet across, of two kinds of hypers- 

 thene-augite andesite, which are referred to genus i of that sub- 

 class. One is a compact grey rock (sp. gr. 272) carrying pheno- 

 crysts both of rhombic and monoclinic pyroxene, the former 

 prevailing, and displaying a small amount of interstitial glass. 

 It is magnetic and exhibits marked polarity, as noticed in Chapter 

 XXVI. The other is a scoriaceous rock containing numerous 

 round steam-pores, ranging up to 5 millimetres in diameter and 

 generally filled with clear quartz-crystals and lined by chalcedony. 

 It contains semi-opaque glass in abundance, and is apparently a 

 semi-vitreous form of the rock just described. Both rocks are to 

 some extent altered. . . . On the crest of a spur, 500 feet below 

 the summit, is exposed in position an augite-andesite, assigned to 

 genus 13, sub-genus i, species B, of that sub-class. It is non- 

 scoriaceous and exhibits a considerable amount of greenish altera- 

 tion products. (Sp. gr. 279.) 



The Avuka Range 



This high range, which lies immediately to the east of Lambasa, 

 attains its greatest elevation in Mount Avuka, which is 1,976 feet 

 above the sea. It represents the extension northward to the coast 

 of the inland Thambeyu mountains that culminate in Mount 

 Thurston. In its upper portion Mount Avuka presents bare 

 precipitous faces apparently of agglomerates and some hundreds 

 of feet in height. My acquaintance with this range is scanty. In 

 a traverse from Lambasa to Ngele-mumu I crossed it a mile or 

 more south of Mount Avuka, where it is only 700 feet in elevation. 



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