Art. XXXIX.—Note on Rock collected by the Rev. W. S. Green from near the Summit of Mount Cook.
[Read before the Wellington Philosophical Society, 9th January, 1889.]
Dnder the microscope this rock is found to be composed of—(1) angular fragments of rather clear quartz, commonly less than 0·1in. in diameter, but occasionally as large as 0·15in.: (2) rather earthy-looking fragments of about the same size, which on examination with a high power are found to be crowded with filmy microliths, often faintly tinged with green, giving
bright colours with the crossed nicols; these about equal the quarta in quantity, sometimes the one, sometimes the other predominating; very probably they are fragments of a decomposed felspar, but some may be bits of an argillite: (3) fragments of well-preserved felspar: (4) some fragments of a rather fibrous brown dichroic mineral, probably biotite: (5) two or three fragments of a filmy green mineral, probably an altered form of (4): (6) a white mica. The microscopic aspect of the rock would suggest that it was a quartzite; but the microscope shows no marked deposition of secondary quartz, or any indication of metamorphism, so that it must be named an indurated, rather felspathic grit. It is not likely to be an Archæan rock, but has probably derived its materials from rocks of that age, being itself very possibly Palæozoic. There is no very definite indication of either a laminated or a cleaved structure.