The Nawavi Range.
With this remarkable coast range, which fronts the Mathuata sea-border for a distance of 12 or 13 miles between Ravi-ravi Point and Nanduri, I have unfortunately but scant acquaintance. It attains its maximum elevation in Mount Nawavi of 2,238 feet, and is described by Mr. J. P. Thomson,[[60]] who surveyed this coast, as broken in two nearly opposite Niurua, the pyramidal mountain of Koro Navuta rising in the gap. Various other peaks, besides that of Nawavi, are marked in the latest Admiralty chart; they vary in height from 1,000 to 1,700 feet. As this range lies only a mile or less back from the beach, it gives to the sea-border a bold and often precipitous appearance, which is well shown in an illustration in Wilkes’ Narrative of the United States Exploring Expedition (iii. 226).
Basic rocks probably prevail in this range. When I ascended its eastern spurs from Nanduri, and reached a height of 800 feet, only basic tuffs and agglomerates came under my notice. From Dana’s remarks[[61]] it is to be inferred that the “frowning bluffs” opposite Mathuata Island are of similar formation; and it would seem that the rugged black stones, described in the Admiralty Sailing Directions[[62]] as topping the hills behind Ravi-ravi Point, are of the same basic character. From its contour and profile I would gather that, as in the great mountainous ridges that constitute the backbone of the island between Va Lili and Mount Thurston, palagonitic tuffs and clays of submarine origin will, together with volcanic agglomerates, be found far up the slopes of this range, and that the axis will prove to be largely composed of massive basic rocks.
The hot springs referred to by Thomson and others as occurring at the foot of the north and south slopes, namely at Vatuloaloa, Nambuonu, and in another unnamed inland locality, are briefly mentioned on page [31].
The Sealevu Divide.—This broad range which separates the Ndreketi and Lambasa basins is an offshoot from the central mountains at Sealevu and reaches the coast just east of Nanduri. Its highest part according to the elevation given in the Admiralty chart is 1,437 feet. The road from Sealevu to Nanduri, which crosses its broad level summit for a distance of about three miles, does not rise over 1,100 feet. Between 800 and 1,100 feet are exposed calcareous tuffs and clays all largely made up of palagonitic materials. The coarser might be described as sandstones. The clays have 12 per cent. of lime and are foraminiferous and are of the type described on page [321]. The rocks displayed on the lower northern slopes on the way to Nanduri are at first the same submarine deposits, and afterwards decomposing basaltic andesites. It is apparent that in the central elevated part of this range there are hills of volcanic formation more or less completely buried beneath these deposits.
The District between Nanduri Bay and Wailevu River
The sea-border between Nanduri Bay and Middle Point, nearly four miles to the east, consists of a fringe of lowland margined by the mangrove-belts and banked by a line of hills between a quarter and two-thirds of a mile inland. These hills form a continuation of the Nawavi coast range of mountains extending from Ravi-ravi Point to Nanduri. They attain their greatest height in the case of Ulu-i-sori, a cockscomb-like peak 1,141 feet above the sea. Another of these hills, Vatu-tangiri, is capped by a remarkable obelisk-like rock. Behind this coast range lies a hill with an elevation of nearly 1,400 feet.
The rocks exposed for the first mile or two along the coast east of Nanduri are agglomerates and basic tuffs. The blocks of the agglomerates, however, are made of an altered grey porphyritic rock which has the characters of a porphyrite of a rather acid type.[[63]] This composition of the agglomerate is quite exceptional and indicates the antiquity of the volcanic rocks in this locality. Farther along the coast the typical agglomerates occur, where the blocks, 3 to 10 inches across, are composed of the usual semi-vitreous black basaltic rock showing plagioclase phenocrysts. Nearer Middle Point a decaying doleritic basalt is displayed at the surface. It is similar to the prevailing rock of the Ndreketi plains, and is referred to the ophitic rocks forming genus 9 of the augite-andesites.
The elevated promontory of Middle Point is a prolongation of a spur of Ulu-i-sori. Where it is crossed by the road it is about 350 feet above the sea. On its west slopes are exposed yellowish-white tuff-like rocks, evidently the prevailing basic clay-tuffs which have become bleached through the hydration accompanying the weathering process. Beneath these deposits lies an amygdaloidal augite-andesite which is bared in places. The rock is semi-vitreous and the amygdules it contains are often a centimetre long. They are composed of a white mineral with fibro-radiate structure and made up of needle-like prisms. It gives off water, but it is not easily fused, and does not gelatinise in HCl.
From the top of the promontory the road strikes inland in an east-south-east direction for Tambia, passing inside the coast range, which is here 600 feet in height, and descending gradually through a region of basaltic andesite into the valley of the Tambia river. (This rock, which has a specific gravity of 2·84, displays more or less parallel stout felspar-lathes, ·23 mm. in length, and has a little interstitial glass. It belongs to genus 13 of the augite-andesites.) Low hills shut in the little valley on all sides except where the river breaks through the coast range. The town of Tambia is not over 100 feet above the sea. About a mile to the north exist hot springs of considerable extent which are described on page [32].