This series of monographs represents continuation on an inter­ national basis of the previous series MINERALOGIE UND PETRO­ GRAPHIE IN EINZELDARSTELLUNGEN, published by Springer­ Verlag. The voluminous results arising from recent progress in pure and applied research increase the need for authoritative reviews but the standard scientific journals are unable to provide the space for them. By their very nature, text-books are unable to consider specific topics in depth and recent research methods and results often receive only cursory treatment. Advanced reference volumes are usually too detailed except for experts in the field. It is often very expensive to purchase a symposium volume or an "Advances in . . . " for the sake of a specific review chapter surrounded by volume unrelated chapters. We hope that this monograph series will by­ pass these problems in fulfilling the need. The purpose of the series is to publish reviews and reports of carefully selected topics written by carefully selected authors, who are both good writers and experts in their scientific field. In general, the monographs will be concerned with the most recent research methods and results. The editors hope that the monographs will serve several functions, acting as supplements to existing text-books, guiding research workers, and providing the basis for advanced seminars. W. VON ENGELHARDT, Tiibingen July 1970 T. HAHN, Aachen R. RoY, University Park, Pa. J. W. WINCHESTER, Tallahassee, Fla. P. J. WYLLIE, Chicago, Ill. Preface Sub-series on "Isotopes in Geology".