We may infer from the above description of this peninsula that it has a history similar to that of most other parts of the island. There is evidence in the upraised reefs and in the “Globigerina” clays and limestones of considerable submergence at one period; and it is highly probable that the prevailing basaltic andesites are the products of submarine eruptions. In my account of the hot springs given on page [26], reference is made to the absence of any trace of a crateral cavity in that locality. The same is true, as far as my observation goes, of the whole peninsula. Altered rocks do not occur in the vicinity of the springs, but they are to be found at distances a mile and more away. It does not seem possible to restore in imagination the original form of this part of the island. The present contours are the results of more than one reshaping of the surface through the agencies of marine erosion and sub-aerial denudation.

The District Between Naindi Bay and the Salt Lake

Three or four of the peaks of this hilly district rise to about 1,000 feet or rather over, the highest being that of Na Suva-suva, which attains a height of 1,110 feet. Since my acquaintance with this region is incomplete, I will confine my remarks to the localities actually examined.

Through the kindness of Mr. F. Spence, I was able to make use of a track cleared to the top of Na Suva-suva. This eminence, which forms a conspicuous landmark for many miles, both landward and seaward, has a rounded summit and is to all appearance an old volcanic neck. It is composed in mass in its upper half of a heavy dark olivine-basalt (sp. gr. 3·01), seemingly non-columnar, and referred to the highly basic rocks forming genus 16 of the olivine-basalts. There is such a thick soil-cap on the lower slopes that I was unable to ascertain the character of the rocks there. It is, however, noteworthy that a very similar olivine-basalt (sp. gr. 2·99) crops out on the coast south of this hill and to the east of Naindi Bay. They both contain abundant small olivine-phenocrysts and a little residual glass, the felspar-lathes averaging ·1-·14 mm. in length. Since their localities are rather more than a mile apart, it is not possible to say without a further examination of the locality whether or not we have here the same intrusion.

On the coast between Naindi Bay and Salt Lake Passage, calcareous tuffs, probably fossiliferous, are occasionally exposed in the low spurs descending to the sea, whilst islets of elevated reef-rock front the beach.

The coast immediately west of the Salt Lake Passage is of exceptional interest. Here the sea-cliffs and the shore-flat are formed of an agglomerate tuff penetrated in all directions by veins of calcite, an inch and under in thickness. The matrix of this deposit, which is a little calcareous, is principally made up of fragments, ranging up to 3 or 4 millimetres in size, of vacuolar palagonite, the minute vesicles being filled with some alteration product. It also contains large macled augite crystals 5 or 6 mm. in size, which can be picked out in numbers by the fingers. The blocks vary from a few inches to two feet across, and are usually composed of an augite-andesite, containing large porphyritic crystals of augite, and are often amygdaloidal, the amygdules, 3 or 4 mm. in size, being formed of a zeolite. But blocks of very different rocks also occur in this agglomerate tuff. One, about two feet across, was composed of a coarsely crystalline diorite made up, as described on page [251], of large crystals of hornblende, 2 to 2·5 centimetres long, and of large opaque crystals of acid labradorite. Another was made of hornblende-hypersthene andesite belonging to the ortho-phyric order of that sub-class (see page [299]). There is a little altered glass in the groundmass, and large secretions of brown hornblende, more than an inch in size, are to be observed in the rock.

It is probable that this singular deposit represents a submarine accumulation of materials ejected from some neighbouring vent. Organic remains did not come under my notice; but apart from the palagonitic character of the matrix and the abundance of veins of calcite, the submarine origin is indicated by the existence of upraised reefs in the coast districts east and west of this locality. The block of diorite affords an important clue as to the character of the deep-seated plutonic rocks in this part of the island. A similar diorite was found by me amongst the blocks in the bed of the Vunimbua River; and on page [185], reference is made to the probability of such rocks forming the nucleus of the Valanga Range.

The hills on the west side of the Salt Lake are worth further examination. On the coast of the Natewa Bay side of this district, in the vicinity of Vuni-tangaloa and between that place and Vuni-sawana, there are displayed agglomerates formed of blocks of hornblende-andesite, some of the specimens being very similar to that obtained from the block of hornblende-andesite noticed in the agglomerate-tuff on the neighbouring south coast.

The Salt Lake

The low isthmus, about 2½ miles in breadth, which connects the Natewa Peninsula with the rest of the island, can be crossed without rising more than 40 or 50 feet above the sea. From the occurrence of upraised reefs in the islets and in the low sea-cliffs of the south coast it may be inferred that at no distant period in the history of Vanua Levu this isthmus was submerged.