From Naithombothombo Point to Undu Point, representing the length of the island (98 miles).
The Natewa Peninsula from the Salt Lake to Kumbalau Point.
The two conical peaks of Vatu Kaisia (1,880 feet) and Na Raro (2,420 feet), which rise up so unexpectedly in the region immediately east of the Ndrandramea district, are also of acid andesitic rocks, in the last case approaching the dacitic type. They lie within the borders of the area of basic tuffs, basic agglomerates, and basic massive rocks, that here begins and extends eastward to Mount Thurston and a little beyond. East of Na Raro there is a gap or break in the profile, where the greatest elevation is probably not over 800 feet; and on its farther side rises up the mountain of Va Lili (2,930 feet), a lofty inland ridge that lies towards the southern coast. Palagonite-tuffs and agglomerates are the prevailing surface-formations in this district.
Eastwards from Va Lili extends for eight or nine miles a lofty, level-topped, and almost peakless range, which I have called the Korotini Table-land, after the towns once situated on its southern slopes. Its outline is shown in the background of the view facing page [153]. It is, however, not so level-topped as it appears to be; but the gradual variations in elevation between 2,000 and 3,000 feet, when spread over a length of some miles, are more or less lost in the general outline of the range as viewed from the coast. Basic agglomerates are principally exposed on the lower slopes; whilst higher up, reaching often to the summit of the table-land, occur palagonite-tuffs containing tests of foraminifera and molluscan shells, massive basic rocks being exposed in places.
The level profile of the Korotini tableland gives place, as one proceeds eastward, to the broken outline of the several lofty peaks of Mariko (2,890 feet), Mbatini (3,437 feet), Thambeyu (3,124 feet) and others.[[4]] Each of these peaks marks one of the bold mountain-ridges that form such a striking feature in the surface-configuration of this part of the island. On the slopes of these ridges, and often also on their summits, appear basic agglomerates and palagonitic tuffs and clays often inclosing tests of foraminifera; whilst exposed in the gorges and protruding at times through the tuffs and agglomerates on the crests of the ridges are displayed massive basic rocks of the type of the hypersthene-augite andesites.
East of Thambeyu the level sinks to about 1,000 feet above the sea, and beyond rises an irregular group of hills and mountains which attain their greatest height in Nailotha,[[5]] 2,481 feet above the sea. We are now near the limit of the area of basic rocks. Following the profile as it slopes away, marked by occasional peaks and breaks, towards Undu Point, we pass at first over a district where basic rocks are mixed with those of more acid type; but before we reach Mount Thuku we enter the district of oligoclase-trachytes, quartz-porphyries, and rhyolitic tuffs, that extends to the extremity of the Undu promontory.
There remains to be noticed the profile of the Natewa Peninsula. As shown in the diagram, this level begins at a few feet above the sea in the vicinity of the Salt Lake; and as it proceeds eastward it attains a level of 1,960 feet in Ngalau-levu and of 1,540 feet in the Waikawa promontory, finally culminating, as it nears Kumbulau Point, in a mountainous district which attains its greatest elevation of 2,740 feet above the sea in the lofty ridge of Ngala, the Mount Freeland of the chart. Altered basic rocks prevail in this peninsula; but more acid andesites also occur, and foraminiferous tuffs and clays are exposed on the slopes, reaching to over 1,000 feet above the sea.
I will conclude this reference to the profile of the island with the remark that if I had neglected to indicate here the close connection that exists between the nature of the surface-configuration and the character of the prevailing rocks I should have ignored a means of investigation which has proved of the greatest value. The rock and surface characters go together. The inland plateau now upheaved 1,000 feet above the sea, was built up by submarine flows of basaltic lava. The isolated conical peak that so unexpectedly intrudes itself into the view is the dacitic core of some submarine volcano long since stripped of most of its fragmental coverings. The lofty mountain-ridges that run athwart the island’s breadth, with their summits usually in the rain-clouds received their coverings of tuffs and agglomerates ages ago when they were submerged; and now they rise to heights of over 3,000 feet above the sea. Bound up with the mysterious origin of these great ridges is the history of the island of Vanua Levu.