Like the writing of most professional archeologists, mine has been confined to so-called learned papers. Good, bad, or indifferent, these papers were in a jargon that only my colleagues and a few advanced students could understand. Hence, when I was asked to do this little book, I soon found it extremely difficult to say what I meant in simple fashion. The style is new to me, but I hope the reader will not find it forced or pedantic; at least I have done my very best to tell the story simply and clearly. Many friends have aided in the preparation of the book. The whimsical charm of Miss Susan Richert's illustrations add enormously to the spirit I wanted. She gave freely of her own time on the drawings and in planning the book with me. My colleagues at the University of Chicago, especially Professor Wilton M. Krogman (now of the University of Pennsylvania), and also Mrs. Linda Braidwood, Associate of the Oriental Institute, and Professors Fay-Cooper Cole and Sol Tax, of the Department of Anthropology, gave me counsel in matters bearing on their special fields, and the Department of Anthropology bore some of the expense of the illustrations. From Mrs. Irma Hunter and Mr. Arnold Maremont, who are not archeologists at all and have only an intelligent layman's notion of archeology, I had sound advice on how best to tell the story. I am deeply indebted to all these friends. While I was preparing the second edition, I had the great fortune to be able to rework the third chapter with Professor Sherwood L. Washburn, now of the Department of Anthropology of the University of California, and the fourth, fifth, and4 sixth chapters with Professor Hallum L. Movius, Jr., of the Peabody Museum, Harvard University. The book has gained greatly in accuracy thereby. In matters of dating, Professor Movius and the indications of Professor W. F. Libby's Carbon 14 chronology project have both encouraged me to choose the lowest dates now current for the events of the Pleistocene Ice Age.