Page:Transactions NZ Institute Volume 15.djvu/511

Oligoclase, 2 …Al S̈i³ + (Ṅa, Ċa)² S̈i³, is mentioned by Dr. v. Haast in quartz porphyries of Mt. Misery and Malvern Hills (Jurors' Rep. N.Z. Ex., 1865, p. 257), and R. Daintree, Esq., F.G.S. (Trans. N.Z. Inst., vol. vii., p. 458), mentions the occurrence of a plagioclase felspar, which is probably oligoclase, in granite from Snowy Peak Range.

Obsidian is mentioned, by Dr., v. Hochstetter, with rhyolites in the Taupo district (New Zealand, Eng. ed., p. 407); by Dr. v. Haast, on the sides of trachytic dykes (selbands) in Banks Peninsula (Jurors' Rep. N.Z. Ex., 1865, p. 257, and Trans. N.Z. Inst., vol. xi., p. 504); and by Mr. J. A. Pond, in the volcanic rock from Mr. Firth's well near Mt. Eden, Auckland (Trans. N.Z. Inst., vol. vii., p. 406). Its distribution in the North Island is widespead in the volcanic regions which occupy the central and north-east portions of the island; but, so far as I am aware, no solid flöes have been discovered, and the mineral has only been found in isolated blocks. It was formerly largely employed by the Maoris for the manufacture of weapons and implements. There are several specimens in the collection of the Colonial Museum from Taupo and White Island.

Pumice.—Is found throughout the volcanic region of the central portion of the North Island whence it is brought down to the sea by rivers, and distributed along the coast by the action of the tides and currents. It is mentioned by Dr. v. Hochstetter (New Zealand, Eng. ed., p. 43) as occurring in plateaux round Lake Taupo, 2,000 feet above the sea and he states (p. 384) that Mr. Grace's house is built of it. It is mentioned (Jurors' Rep. N.Z. Ex., 1865, pp. 35, 253) from the beach near Napier, where it is found in considerable quantities, brought down by the rivers from the north and also from Waikato, and Mr. J. C. Crawford (Trans. N.Z. Inst., vol. vi., p. 356) states that it occurs in large quantities at Tokano and (Trans. N.Z. Inst., vol. viii., p. 377) that pumice floats down the Wanganui River in such quantities that it would be easy for a ship, anchored in the river, to put out nets and so load the ship. Around the volcanic group of Ruapehu and Tongariro there are immense areas covered with pumice, and at Kereru, Napier, and many other localities on the east coast of the North Island, there are extensive deposits of compact white pumice-sand, which are mentioned by Mr. McKay (Geol. Rep., 1876–77, p. 81).

Pitchstone.—The only district in New Zealand where this mineral occurs is between Mt. Somers and Snowy Peak, where it is associated with quartz porphyries of which it appears to be the vitreous form, a complete series representing the change from a fluid pitchstone, through various stages, to a quartz porphyry with felsitic base and small crystals of quartz and garnet in which no fluxion structure is visible. It is of all colours, from grey to