Everyone working in a problem as complex as continental drift, must at some time have feit the need for an objective data summary in fields other than his own. It is a scientific dilemma that, aIthough there is evident need for researchers with competence in many fields (the classical natural scientist), the time in volved in acquiring such broad experience is so great as to ren der the task largely impossible. The alternative seems to be the team approach, and we have espoused it in tbis volume. Editors and contributors alike have tried in this book to keep the accent upon factual information and to reduce interpretation to a minimum. Interpretation there must be, however, since without it science is but an inteHectual pastime comparable to pbilately. The librarian's need to classify results in the appearance of our names upon the spine oftbis volume, however, we would like to make it clear that the book has been a truly cooperative effort and could not have succeeded but for the active help of the individual contributors, whose assistance seldom was re stricted to their chapters. Special thanks must be given to our South American coHeagues, for the tolerance with which they viewed out editorial attempts, and to Dr. E. Machens, for his careful review of the translation of his manu script. We wish also to acknowledge the help of Dr. C. W.