Na Raro.
In Na Raro we have one of the most interesting of the isolated hornblende-andesite mountains of Vanua Levu. Unlike Vatu Kaisia, which often eludes the observation, Na Raro is visible from most points of view. It is double-peaked, the two peaks lying in a north and south line and rising precipitously. It is this feature that gives the mountain such a variety in its profile. From the north and south it appears as shown in the accompanying sketch as a sharp conical peak. From the north-east and south-east, as illustrated in the two other sketches, it has the form of a blunt or square-topped mountain; and its true shape is only shown when it is seen from the east or west. In the photograph here reproduced which was taken about 1½ miles to the south-west, the two peaks are with difficulty distinguished. (See [frontispiece].)
Not many ascents have been made of these precipitous peaks. Mr. A. Barrack, who kindly supplied me with some information about it, made the ascent some years ago; and Mr. Blyth (?), a magistrate, also reached the top. There are stories of some big officials being hauled up in baskets; and the natives told me of a white man who was seized with a shivering-fit when he arrived at the summit. It is certainly a rather hazardous climb; but the safest plan is to resign oneself into the hands of the natives, who “bundle” one up in an expeditious, if not in a very ceremonious, fashion. Nareilangi, near the foot of the mountain on the north side, is a convenient starting-point, and half a dozen stout Fijians will not prove too many to assist the climber in the difficult parts of the ascent. Since the top usually becomes clouded as the day progresses, it is best to spend a night in a cave about 1,400 feet above the sea from which the ascent can be made in the early morning. The view from Na Raro is panoramic and extends over a large part of the island from Naivaka to Savu-savu.
From the south off Kumbulau Point.
From the north in the Ndreketi Plains.
From the North-east.
From the East-south-east.
Na Raro rises up to a height of 2,420 feet in the midst of a region of basic rocks. Agglomerates and coarse tuffs formed of aphanitic augite-andesites prevail in the broken country on the north and west sides towards Nareilangi and Ndrawa. Immediately south rises the Tavia Range with its basaltic andesites and overlying palagonite-tuffs; whilst on the east lies a spur of this range.
Nareilangi, the village from which the start is made, is about 2½ miles distant from Na Raro, and though situated in the heart of the island it is only about 100 feet above the sea. The track first passes through a district of foraminiferous tuffs and clays reaching up to 200 or 250 feet. Afterwards a broken country extending up to 800 feet is traversed. Here prevail agglomerates and tuff-agglomerates derived from aphanitic augite-andesites.[[58]] One then descends into a valley about 600 feet above the sea, and from this place the ascent of the mountain proper begins.
The ascent at first is fairly steep, dacitic tuffs prevailing up to 1,000 or 1,100 feet above the sea and forming in places precipitous cliff-faces. Large masses of hornblende-andesite lie on the slopes. The dacitic tuffs distinguish Na Raro from all the other peaks of hornblende-hypersthene-andesite rocks that I examined. They seem generally to have been stripped off by the denuding agencies; and only at times, as around the slopes of Ndrandramea and Thokasinga, are to be found the remains of agglomerates of the same formation. In the case of Na Raro, however, the tuffs differ somewhat in their components from the rocks forming the mountain mass. The tuffs are derived from a hornblende-andesite of dacitic type; whilst the massive rocks of the mountain are of hornblende-hypersthene-andesites, without porphyritic quartz, but approaching the dacitic habit.
The tuffs of Na Raro, which are sometimes compacted and at other times rather friable, do not display bedding. They contain a little lime; but I found no tests of foraminifera. They are composed of fragments, up to a centimetre in size, of a dacite displaying brown hornblende, plagioclase, and quartz in a microfelsitic groundmass, together with a few fragments of a semi-vitreous basic andesite.
Above 1,100 feet the tuffs give place to the massive hornblende-hypersthene-andesite. At an elevation of 1,450 feet, a shoulder of the mountain is reached, near the top of which is the cave above mentioned. Crossing the shoulder one descends for 100 or 150 feet into a gap, thus reaching the foot of the precipitous northern peak, which rises up like a wall for a height of from 900 to 1000 feet overhead. It is in mass of the andesite just mentioned, many of its faces presenting inaccessible cliffs displaying seemingly no structure. This peak is somewhat lower than the southern peak. I placed its height at 2,270 feet, which, taking the total elevation of the mountain at 2,420 feet, as given in the chart, makes the difference 150 feet. A deep and broad cleft, that goes half-way down the mountain, separates the two peaks. The southern one, which appears to be inaccessible, is evidently formed of the same acid andesite.
These hornblende-andesites, with or without porphyritic quartz, appear to be for the most part restricted to the immediate vicinity of Na Raro, except to the south-west, where at a distance of about a mile and a half from the mountain at an elevation of 500 feet occur a rubbly hornblende-andesite and agglomerates of the same materials. Though the rock is of the Na Raro type, its presence here is suggestive of a distinct vent of small size, of which most of the traces have been swept away during the emergence of the island. About half a mile south-east of this locality at an elevation of 450 feet occur some singular banded palagonite-tuffs which, although they do not show foraminifera in the section examined, contain a little calcite and are probably of submarine origin.... In this locality I found a large white mass, measuring 4 × 4 × 5 feet, formed of a siliceous rock appearing in thin sections as granular chalcedonic quartz (see page [355]).
The hornblende-andesite of Na Raro, as in the case of the rocks of most of the other peaks of acid andesites, has its peculiar characters. It differs, for instance, from that of Vatu Kaisia in the larger grain of the felsitic groundmass (N. R. ·021 mm.; V. K. ·013 mm.), in the absence or rarity of phenocrysts of rhombic pyroxene, in its lower specific gravity (2·6 N. R.: 2·7 V. K.), in the presence of a little interstitial glass, and in other particulars. Both, however, belong to the sub-class of hornblende-hypersthene-andesites, and are described on page [301]. In the Na Raro rock the rhombic pyroxene is represented in the groundmass.
With regard to the relative age of Na Raro I am inclined to think that it is the most recent of the acid andesite peaks of the island. Neither vitreous nor vesicular rocks came under my notice in its vicinity; whilst the tuffs that clothe its lower slopes are non-pumiceous, though of dacitic origin, but containing also a few fragments of a semivitreous basic andesite showing tiny felspar lathes and augite-granules. Since the everywhere prevailing submarine palagonite-tuffs and foraminiferous clays do not extend over its area, we may assign to it a later date. It is evidently also posterior in time to the basaltic andesites and aphanitic augite-andesites around, which are covered by these submarine deposits. Relatively recent as it apparently is, this mountain bears the impress of a high antiquity. There is nothing to indicate that this “core” of a volcanic mountain belonged to a subaerial vent. Na Raro has shared in all the later stages of the submergence and emergence of the island. Though it presents the final page in the history of the hornblende-andesite volcanoes, that chapter has been for unknown ages closed.
The Na Raro Gap.—Between the Tavia and Va-lili Ranges there is a break in the mountainous backbone of the island, to which I have given this name. The greatest elevation is probably not over 800 feet. It is from the south side of this watershed that the Lango-lango river takes its rise.