On the Polysynthetic Structure of some Porphyritic Quartz Crystals in a Quartz-felsite

Abstract

Before describing some features of special interest in the microporphyritic quartz crystals of an Indian felsite, it may be as well to say a few words, by way of preface, regarding the rock itself.About 85 miles to the north-west of the town of Delhi, in the peninsula of India, a hill rises abruptly from the plain to the height of 630 feet. It is one of a series of similar elevations separated from each other by some miles of sandy soil which strike the traveller with their resemblance to a group of islands in a tempestuous sea—an idea greatly favoured by the long swelling waves into which the sand is thrown by the strong westerly winds which prevail in that region during the greater part of the year.