2i6 A NATURALIST IN THE PACIFIC chap. 



Jected to alteration after the development of the columnar structure 

 and before the deposition of the overlying clay-tuffs or "soap- 

 stones," which are no doubt of submarine origin. These sedi- 

 mentary tuffs belong probably to the period when the submarine 

 agglomerates and palagonite-tuffs of the neighbouring peak of 

 Vungalei were formed. 



(c) Traverse of the coast range from Nandongo to Vanuavou on 

 the shore of Natewa Bay. — This route was taken by Mr Home, 

 the botanist, in 1878. I approached Nandongo from Tembe to 

 the northward. The road at first lay between hills about 700 feet 

 in height displaying in their precipitous faces agglomerates 

 overlying fine sedimentary tuffs. These deposits in the form of 

 slightly calcareous basic tuff-clays, the so-called " soapstones," are 

 exposed in the bed of the Wainikoro River as one nears Nandongo. 

 This village, which is situated on the headwaters of the Wainikoro 

 at an elevation of about 180 feet above the sea, lies near the foot of 

 the range. In its vicinity there is a small thermal spring which is 

 referred to on page 33. 



Proceeding south from Nandongo one notices in the stream- 

 course at the foot of the slopes the sedimentary tuff deposits above 

 mentioned, bedding and dipping gently to the west. Farther up 

 the slopes, higher than 250 feet above the sea, there are exposed 

 the deeper-seated rocks of the range in the shape of compact red- 

 dish rocks (sp. gr. 2*48), which appear under the microscope to be 

 highly altered acid andesites or oligoclase-trachytes originally 

 displaying flow-structure and a fair amount of glass, but now much 

 disguised by the formation of secondary quartz. On this north 

 slope of the range I also found an amygdaloidal variety of the same 

 altered rocks containing irregular amygdules, 5 or 6 millimetres 

 long, of fibrous quartz or chalcedony. Blocks of basaltic andesite 

 were observed on the summit, which has an elevation of 950 to 

 1,000 feet. On the southern slopes descending towards Natewa 

 Bay coarse basic tuffs together with blocks of basaltic andesite are 

 chiefly exposed. The last-named probably represent dykes both 

 on the south slope and on the summit. The rocks exhibited on the 

 portion of the coast of Natewa Bay corresponding to this range 

 are dark and light-coloured sedimentary tuffs usually calcareous, 

 with occasional basaltic andesites indicating dykes. . . . From this 

 traverse it would appear that the range has an axis of altered acid 

 rocks overlain by basic sedimentary tuffs and pierced by basaltic 

 dykes. 



{d) The mountainous district lying between the head waters 



