The Coast between the Mouth of the Ndreke-ni-wai River and the Foot of the Ngala or Mount Freeland Range.—Between this estuary and Valavala, two miles to the eastward, occurs a bedded calcareous palagonitic tuff of sedimentary origin, dipping steeply to the north. In one locality there is a rudely columnar dyke of a porphyritic augite-andesite. Coarse basic tuffs exposed in the cliffs and shore-flat of Ko-nandi-nandi Point on the side of Valavala Bay display a spheroidal structure, due probably to the vicinity of some igneous intrusion. The sea-border extending from this bay to Natewa, and farther on to Waikatakata, near the foot of the Ngala mountains, is in most parts a broad low strip of coast-land, where rock-exposures are infrequent. A dark grey andesite forms the blocks of the agglomerate in this locality. It is noticeable on account of the prismatic pyroxene of the groundmass; and it is assigned to genus 5 of the second (prismatic) sub-order of the hypersthene-augite andesites. A blackish semi-vitreous pyroxene-andesite occurs in the vicinity of Natewa.
At Waikatakata (the Fijian word for “hot water”), where an outlying spur of the Mount Freeland or Ngala Range reaches the coast, hot springs issue on the hill-side, as described on page [34]. On the slopes around the springs lie huge masses of an aphanitic basaltic andesite having a specific gravity of 2·81 and referred to genus 16 of the augite sub-class. It displays a characteristic andesitic groundmass, showing crowded felspar-lathes in flow-arrangement with average length of ·17 mm., and containing scarcely any residual glass.
Proceeding along the coast east of Waikatakata, one enters the region of altered pyroxene-andesites, for which Mount Freeland, or the Ngala Range, is remarkable. There are first to be observed on the shore blocks of a grey altered ophitic dolerite, which belongs to the non-porphyritic division of genus 10 of the augite-andesites and is described in detail on page [275]. Afterwards the characteristic rocks of the district occur. The lofty spurs of the Ngala Range here reach the shore; and between them lies the coast village of Ngara-vutu, from which the ascent to the summit is best made.
Mount Freeland or the Ngala Range
This high range forms a conspicuous object in the profile of this part of the island. It derives its Fijian name from the old war-town of Ngala that was situated at an elevation of 1,500 or 1,600 feet overlooking Ngara-vutu on the west. The main mass of the range takes a crescentic sweep, 3 or 4 miles in extent and facing Natewa Bay. It incloses the coast district of Tunuloa. The steep mountain-slopes here rise to 2,000 feet and over, the greatest elevation being 2,740 feet. The densely wooded spurs of the range occupy most of the area between the town of Natewa, Kumbulau Point, and Mbutha Bay.
The summit is a long narrow ridge covered with a dense entangled mass of Freycinetia stems which render progress very difficult. The rocks exposed all the way up from the stream-courses in the vicinity of Ngara-vutu to the top, are almost all of the same type, namely altered augite-andesites. They are dark grey in colour and effervesce slightly with an acid, whilst occasionally they show a little pyrites.[[90]] Agglomerates were not observed and tuffs only in one locality, 1,200 feet above the sea, where a highly altered tuff composed of debris of the prevailing rocks was exposed. At an elevation of 500 feet there occurred a grey doleritic porphyritic rock, displaying large opaque crystals of plagioclase, and looking like a porphyrite. It exhibits a semi-ophitic groundmass, and is probably an intrusive mass. A description of it will be found under genus 10 of the augite-andesites (page [274]).
The general petrological characters of the principal summit of Mount Ngala point to its high antiquity as a volcanic mountain. It probably ranks among the oldest extinct volcanic vents in the island.
Proceeding along the coast from Ngara-vutu to Navetau, the Buli’s town of the Tunuloa district, one observes blocks of basic rocks. Farther to the eastward for a distance of two or three miles basic agglomerates and basic tuff-agglomerates prevail along the sea-border, being often extensively exposed in the cliff-faces of the hills. The rock composing the blocks is a hemi-crystalline pyroxene-andesite remarkable for the prismatic pyroxene in the groundmass, and referred to genus 17 of the hypersthene-augite sub-class.
I crossed the range to Ndevo on the other side of the peninsula from a place three or four miles west of Kumbulau Point, rising on the way to a height of 930 feet. For the lower 300 feet on the north slope basic agglomerates and basic tuff-agglomerates are exposed. They are made up of the same materials as those above described on the coast. Near and at the summit occur compacted brecciated tuffs made up of palagonitised basic materials but containing no lime, and these are associated with light greenish fine-textured hard tuffs of an acid character, but without lime or organic remains. In this last case the deposit is formed of mineral fragments (oligoclase, rhombic and monoclinic pyroxene, &c.), the debris of a hemi-crystalline volcanic rock, and a quantity of greenish alteration products.
On the south side in the vicinity of Ndevo the sea-border is composed of calcareous palagonitic clays and tuffs containing pteropod shells and large tests of foraminifera in abundance. These deposits, which are horizontally bedded, extend a mile inland and reach to between 250 and 300 feet up the slopes. A hot spring is stated to occur between the tide-marks near Ndevo.