The Journal of geology - 1919 Author:Thomas Chrowder Chamberlin Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: PEGMATITE, SILEXITE, AND APLITE OF NORTHERN NEW YORK1 WILLIAM J. MILLER Smith College, Northampton, Massachusetts INTRODUCTION During twelve... more » seasons of field work in the Adirondack Mountain region of New York, the writer has made many hundreds of observations on bodies of pegmatite, quartz (silexite), and aplite. Certain of the phenomena long proved to be very puzzling, and more recently it has become evident that some generally accepted interpretations of such phenomena are not satisfactory when applied to many of the occurrences in the Adirondack region. While engaged in the detailed geologic mapping of the Lyon Mountain quadrangle, the writer was-soon impressed by the exceptional opportunity for a careful study of the pegmatite, quartz (silexite), and aplite bodies which are there so wonderfully exhibited in countless numbers. Many detailed notes were taken and sketches were made. The North Creek quadrangle, surveyed by the writer some years ago,2 was also revisited for the purpose of making further observations on certain pegmatites there so well exhibited. In this paper the discussions deal almost entirely with the Lyon Mountain and North Creek quadrangles. PEGMATITE, SILEXITE, AND APLITE IN THE GRANITES OF THE LYON MOUNTAIN. QUADRANGLE The granites.- -- Several varieties of granite and granitic syenite constitute the main bulk of the rocks of this district. Among these the variety of chief interest in the present discussion is a fine to medium-grained, usually pink rock varying from a true granite through granitic syenite to quartz syenite or even quartz diorite. In the more typical specimens of granite dark minerals, 1 Published by permission of the state geologist of New York. 2 W. J. Miller, N. Y. State Mus., Bull. 170. except magnetite, a...« less