The statements relating to time have presented the greatest difficulty, as the authorities differ widely, but the dates have been fixed with extreme conservatism and the writer believes that whatever changes in them are hereafter required by further investigation and study, will result in pushing them back and not forward in prehistory. The dates given in the chapter on “Paleolithic Man” are frankly taken from the most recent authority on this subject, “The Men of the Old Stone Age,” by Prof. Henry Fairfield Osborn and the writer desires to take this opportunity to acknowledge his great indebtedness to this source of information, as well as to Mr. M. Taylor Pyne and to Mr. Charles Stewart Davison for their assistance and many helpful suggestions. The author also wishes to acknowledge his obligation to Prof. William Z. Ripley’s “The Races of Europe,” which contains a large array of anthropological measurements, maps and type portraits, providing valuable data for the present distribution of the three primary races of Europe. The American Geographical Society and its staff, particularly Mr. Leon Dominian, have also been of great help in the preparation of the maps herein contained and this occasion is taken by the writer to express his appreciation for their assistance. INTRODUCTION TO THE FOURTH REVISED EDITION The addition of a Documentary Supplement to the latest revision of this book has been made in response to a persistent demand for “authorities.” The author has endeavored to make the references and quotations in this Supplement very full and, so far as possible, interesting in themselves as well as entirely distinct from the text, which stands substantially unchanged, and the authorities quoted are not necessarily the sources of the views herein expressed but more often are given in support of them. The contents of the book, since its first appearance, have had the advantage of the criticism of virtually every anthropologist in America and in England, France and Italy—many of whom have furnished the author with valuable corroborative material. Some of this material appears in the notes, but accessible authorities and the classical writers have been given the more prominent place. The supplement covered, as first prepared, substantially every statement in the book, but much was afterward omitted because it would seem that some things could be taken without proof.