Volcanic Rocks from New Zealand ¹

Abstract

THE district dealt with in this memoir is part of the principal gold-field of New Zealand. The igneous rocks here, which are the source of the gold, are of Tertiary age, though an older series, of Palæozoic age, occurs in the same district. There had been no previous petrographical study of the rocks, of a kind at once cornprehensive and detailed, when a specially made collection of oo specimens was placed in the hands of Prof. Sollas for description, and the report now before us consequently contains much valuable material. Mr. McKay tells us that the principal object of invoking the aid of this well known petrologist was to place the nomenclature of the rocks on a more satisfactory footing. Whatever the object, we are glad to welcome the result, and we also accept gratefully the lavish illustration which attests the liberality of the New Zealand Government. There are upward of 100 plates, reproduced by “process” from photographs, most of them representing thin slices of rocks photographed from the microscope. A figure measuring 7 inches by 5 inches affords a much better conception of the micro-structure of a rock than can be gained from the illustrations in most petrographical memoirs.