Since the book was not the result of personal work in the field, but rather the product of the kind of research that is nothing more than reading and talking, I was in the debt of many men and books, and a welter of papers, pamphlets, and periodicals. I found it hard to believe that in any other branch of science so many overworked men and women would be so ready to give their time to talk and correspondence with the amateur. I was deeply indebted to more than two score who had gone out of their way to answer questions, lend books, or give reprints of papers. In listing them I was more than certain that I had inadvertently omitted some: Edgar Anderson, Ernst Antevs, Ralph L. Beals, Junius Bird, Robert J. Braidwood, Henry J. Bruman, Kirk Bryan, George F. Carter, R. A. Daly, Helmut de Terra, Loren C. Eiseley, Richard F. Flint, James Gilluly, Harold S. Gladwin, M. R. Harrington, Frank C. Hibben, Frederick W. Hodge, Harry Hoijer, Earnest A. Hooton, W. W. Howells, Frederick R. Johnson, Arthur R. Kelly, G. H. R. von Koenigswald, Alex D. Krieger, Alfred L. Kroeber, M. M. Leighton, Theodore D. McCown, George G. MacCurdy, P. C. Mangelsdorf, Paul S. Martin, Hallam L. Movius, Jr., Raymond W. Murray, N. C. Nelson, Charles W. Phillips, Cyrus N. Ray, E. B. Renaud, Frank H. H. Roberts, Jr., Alfred S. Romer, Irving Rouse, Curt Sachs, Carl O. Sauer, E. H. Sellards, Herbert J. Spinden, T. D. Stewart, Wm. Duncan Strong, Griffith Taylor, Bella Weitzner, H. M. Wormington, and Clark Wissler. Next to the scientists who provide knowledge stand the librarians who help to preserve it and make it usable. I was peculiarly indebted to a number of these: Miss Margaret Currier, Librarian of the Peabody Museum, Cambridge; her assistant Miss Jessie Bell MacKenzie; Mrs. Ella L. Robinson, Librarian of the Southwest Museum; Dr. Lawrence C. Powell, Librarian of the University of California at Los Angeles; his most cooperative staff; and particularly one of its members, Miss Hilda M. Gray, whose expeditions into the equal mysteries of stacks and bibliographies saved me many hours of labor and I can’t guess how many blunders. Professor Hester and I add a warm word of thanks to Mrs. Alice De Lisle for assembling data, preparing charts, typing, filing, and research. I was particularly indebted to Frank H. H. Roberts, Jr., of the Smithsonian Institution, the outstanding authority on early man in North America, for his reading, checking, and challenging of the manuscript, and to M. R. Harrington, who read and criticized my first draft. I also owed much to a number of men and women who read various chapters on which they had special knowledge: Edgar Anderson, Ernst Antevs, Robert J. Braidwood, Henry J. Bruman, Loren C. Easeley, James Gilluly, Harold S. Gladwin, M. R. Harrington, Robert F. Heizer, Earnest A. Hooton, Alex Krieger, Alfred L. Kroeber, Theodore D. McCown, Ernest S. Macgowan, Hallam L. Movius, Jr., and H. M. Wormington.