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100 The rock here described from Muri Point wonld, from the complete absence of feldspar, he classed as a nephelinite according to Rosenbusch's scheme. It is retained here amongst the phonolites because its chemical and mineralogical composition show much closer relationship to the phone- Jites than to the basalts.

The Native weapon forwarded by Mr. Brown is of quite different material from the rocks described. The absence of olivine and the abundance of feldspar place it among the angite-andesites. It is quite conceivable that it was made from one of the Tongan rocks.

ArrUTAKI.

Mr. C. Cameron, R. 11., kindly forwarded me samples of rock from this island. The following notes were made by him on the specimens : " Sample A, from the mainland, is fairly common, sometimes in large blocks, and was occasionally used in ancient times for building round the priests' mune. It is casily shattered by fire. Sample B from a small island called Rapoka, in the lagooli, abont a mile from the mainland. It is often used by the women for their native ovens, as it stands fire better than A, though not entirely well."

A. A relatively coarse lasaltie: rock, with much olivine and an abund- ance of idiomorphic augite, and but little feldspar, which is labradorite. The colour of the angite shows that it is strongly titaniferous. No nephelin could be distinguished in section, but the rock-powder gelatinises readily on treatment with dilute HCl, and crystals of salt are formed when the solution is evaporated.

B. Very fine gruined compact rock Olivine is very abundant, and is often stained with limonite on the margin. Augite granular, and restricted to the groundmass, where it is associated with much magnetite and a pre- dominance of minte crystals of nepheline, without sharply crystalline boundaries. The rock is clearly a nephelimite or pepheline-basalt. The accompanying map, copied from the Admiralty chart. shows the form of the island. It is at once seen that the mainland is at the northern side of the interior of the circular coral reef, and is situated near the margin. Rapoka Island is near the south-east portion of the interior of the reef. The form of the island suggests that submergence has taken place, but it may be that the coral reef has arizen on the margin of a shoal forned by wave-action dispersing the material of a loose scoria cone, as has been exemplified in the case of Falcon Island, in the Tonga Group. It will be remembered that this origin has been suggested by Mr. Lister to explain the occurrence of atolls in the southern portion of the Tonga Group of islands, although there is clear evidence of clevation of as much as 1,000 ft. in the north-east portion of the group.

The rocks from Aitutaki are not closely related to any types that I have seen in the south-west Pacific. They resemble the Auckland basanites more closely than any of the others.

EXPLANATION OF PLATES IT AND IT.

PLATE TIL

Sketch-majs of Ruotonga undaki.

PLATE IV

l'ig. 1. Hiero, section of epheline phonolite, Parotonga. The clear portion is nepheline : the dark material is ægirine. Hlagnified 30 diameters, ordinary light.