A manuscript copy, with corrections and editor's notations in red, of the article published in the Philosophical Society of Washington Bulletin, volume 12, 1892.

The Evolution of the Igneous Rocks, by N. L. Bowen, appeared in 1928 and had a profound influence on later generations of petrologists. Drawing on his series of lectures at Princeton University in the spring of 1927, Dr. Bowen identified, outlined, and applied the principles of physical chemistry relevant to petrological processes. Whereas the major petrochemical questions he discussed are still relevant today, the answers appear to change with time. The purpose of the present volume is to provide an updated view of those questions, in the light of almost fifty years of accumulated observations, using the principles Bowen set forth. Originally published in 1979. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

This book is for geoscience students taking introductory or intermediate-level courses in igneous petrology, to help develop key skills (and confidence) in identifying igneous minerals, interpreting and allocating appropriate names to unknown rocks presented to them. The book thus serves, uniquely, both as a conventional course text and as a practical laboratory manual. Following an introduction reviewing igneous nomenclature, each chapter addresses a specific compositional category of magmatic rocks, covering definition, mineralogy, eruption/ emplacement processes, textures and crystallization processes, geotectonic distribution, geochemistry, and aspects of magma genesis. One chapter is devoted to phase equilibrium experiments and magma evolution; another introduces pyroclastic volcanology. Each chapter concludes with exercises, with the answers being provided at the end of the book. Appendices provide a summary of techniques and optical data for microscope mineral identification, an introduction to petrographic calculations, a glossary of petrological terms, and a list of symbols and units. The book is richly illustrated with line drawings, monochrome pictures and colour plates. Additional resources for this book can be found at: http://www.wiley.com/go/gill/igneous.

Our aim in writing this book is to try to show how igneous rocks can be persuaded to reveal some ofthe secrets of their origins. The data of igneous rocks consist of field relations, texture, mineralogy, and geochemistry. Additionally, experimental petrology tells us how igneous systems might be expected to behave. Working on this material we attempt to show how hypotheses concerning the origins and evolution of magmas are proposed and tested, and thus illuminate the interesting and fundamental problems of petrogenesis. The book assumes a modest knowledge of basic petro graphy, mineralogy, classification, and regional igneous geology. It has a role complementary to various established texts, several of which are descriptively good and give wide coverage and evaluation of petrogenetic ideas in various degrees of detail. Existing texts do not on the whole, however, deal with methodology, though this is one of the more important aspects of the subject. At first sight it may appear that the current work is a guidebook for the prospective research worker and thus has little relevance for the non-specialist student of geology. We hope this will prove to be far from the case. The methodological approach has an inherent interest because it can provide the reader with problems he can solve for himself, and as an almost incidental consequence he will acquire a satisfying understanding.

N this book the task of summarising modern petrology I from the genetic standpoint has been attempted. The scale of the work is small as compared with the magni tude of its subject, but it is nevertheless believed that the field has been reasonably covered. In conformity with the genetic viewpoint petrology, as contrasted with petrography, has been emphasised throughout; and purely descriptive mineralogical and petrographical detail has been omitted. Every petrologist who reads this book will recognise the author's indebtedness to Dr. A. Harker and Dr. A. Holmes, among British workers; to Prof. R. A. Daly, Dr. H. S. Washington, and Dr. N. L. Bowen, among American petrologists; and to Prof. J. H. L. Vogt, Prof. V. M. Goldschmidt, Prof. A. Lacroix, and Prof. P. Niggli. among European investigators. The emphasis laid on modern views, and the relative poverty of references to the works of the older generation of petrologists, does not imply any disrespect of the latter. It is due to recognition of the desirability of affording the petrological student a newer and wider range of reading references than is usually supplied in this class of work; for refer ences tend to become stereotyped as well as text and illustrations. Furthermore it is believed that all that is good and living in the older work has been incorporated, consciously or unconsciously, in the newer.