This series of monographs represents continuation on an international basis of the previous series MINERALOGIE UNO PETROGRAPHIE IN EINZELOARSTELLUNGEN, published by Springer-Verlag. The voluminous results arising from recent progress in pure and applied re search 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 met''hods and results often receive only cursory treat ment. 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 . . . " volume for the sake of a specific review chapter surrounded by 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, at reasonable prices, reviews and reports of care fully selected topics written by carefully selected authors, who are both good writers and experts in their scientific field. In general, the mono graphs 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. August 1967 W. VON ENGELHARDT, Tiibingen T. HAHN, Aachen R. Roy, University Park, Pa. J. W. WINCHESTER, Ann Arbor, Mich. P. J. WYLLIE, Chicago, Ill.