File:Transactions of the Royal Society of New Zealand (1911) (14758898376).jpg

Identifier: transactionsofro1911roya (find matches)
Title: Transactions of the Royal Society of New Zealand
Year: 1911 (1910s)
Authors: Royal Society of New Zealand
Subjects: Science
Publisher: Wellington, N.Z. : The Society
Contributing Library: Brigham Young University Hawaii, Joseph F. Smith Library
Digitizing Sponsor: Consortium of Church Libraries and Archives

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r this type of nephelinite is in theAuckland Domain. Here there is no exposure of the rock in the solid,for all the specimens that have been obtained were derived from bouldersejected during the explosive eruptions of the volcano of which the cricket-ground now occupies the crater. This rock has been known for sometime, but the only description hitherto published of it is in a generalpaper by Marshall (8). No analyses of any of these rocks have hithertobeen published. The occurrence of these rocks on the western side of the WaiholaLake is of special interest. Here the rock is extremely coarse overpart of the outcrop (analysis A), and it has a structure that is app;rently granitoid in hand-specimens. Apatite was the first mineral a- Marshall.—Nephelinite Bocks in New Zealand, 305 form in it. The prisms are of considerable size, as much as 1 mm. longand 0*18 mm in diameter. The prisms are not numerous in the olivineor ilmenite, but are abundant in the younger constituents. Ilmenite in
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Mica schists, Maitaisystem (Trias Jura) 8 miles. Geological Structure of Part of East Otago. grains of 1-5 mm. in (diameter is rather frequent, and displa)^ its usualstructure. Olivine is fairly, common in crystals as much as 6 mm. indiameter, and is somewhat serpentinized. The augite is a titaniferous 306 Transactions. variety, with pronounced zonal and hour-glass structure, and with theusual pleochroism, and occasionally shows the steel-blue birefringencedue to the high dispersion of the optic axes. A narrow margin isusually dark green. The mineral is completely idiomorphic. The nephe-line is abundant, For the most part its crj^stallization \vas finishedbefore that of the feldspar. It is largely altered to natrolite. The feld-spar is much twinned on the albite and pericline laws, and has inmany places the appearance of microline. The extinction-angle, however,proves it to be andesine. It was the last of the larger crystals toform. There is here and there a small quantity of groundma

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