Each traverse of the great Koro-tini Range will provide us with new facts to aid us in framing an explanation of the origin of this long mountain-ridge. The principal lesson to be learned from the journey across the range from Waisali to Sealevu, and from the visit to the cliffs, is concerned with the great extent and thickness of these submarine basic tuffs and agglomerates. From 1,000 feet above the sea up to the summit, 2,400 feet in height, they are almost the only rocks exposed, excepting the occasional masses of basaltic rocks, which probably represent dykes. Their maximum thickness must amount to some hundreds of feet.
(2) TRAVERSE OF THE KORO-TINI RANGE FROM MBALE-MBALE TO VANDRANI.—In this traverse the track before ascending to the summit crosses a spur of the Koro-tini Bluff, and then descends into the valley of the Natoarau river on the east side of it. It will therefore be convenient to describe the bluff before giving my description of the journey across the range.
The Koro-tini Bluff is a lofty headland (if I may so term it), lying about four miles inland from the mouth of the Ndreke-ni-wai. It attains an elevation of about 2,000 feet, and terminates above in a line of precipices 300 or 400 feet in height. It represents the southern edge of the level-topped mountain range behind, and like the Sealevu cliffs on the north side it affords a natural section of its mass. It is shown in the plate facing page 153, where it rises at the back of the lagoon.
Approaching the bluff from Mbale-mbale, one crosses a low-lying district less than 100 feet above the sea before striking the spur. Here and in the lower few hundred feet of the spur are exposed basic agglomerates, and occasionally in the mass a semi-vitreous vesicular olivine-basalt, almost like a pitchstone, and displaying large porphyritic crystals of plagioclase, 5 or 6 millimetres long, the agglomerates being made up of the same material. Higher up, at elevations between 1,000 and 1,500 feet, are exposed coarse palagonite-tuffs made up of fragments, usually 1 to 3 mm. in size, of extensively palagonitised basic vitreous rocks, such as occur in the cliffs above. These tuffs become coarser as one approaches the precipitous bluff, the base of which lies about 1,650 feet above the sea. Here the cliffs present a bare rocky face, some 200 feet high. The lower portion is composed of an agglomerate-tuff, and the upper portion mainly of agglomerates. These deposits display no bedding excepting a single plane of division inclined steeply to the north at an angle of perhaps 40°.