1. P. S. Martin and T. E. Wright, Jr., eds. “Pleistocene Extinctions: The Search for a Cause” (New Haven: Yale University Press, 1957).
2. Carl O. Sauer, in “Man's Role in Changing the Face of the Earth,” ed. by William L. Thomas (Chicago: The University of Chicago Press, 1956). See also many other papers in this volume, as well as “Arid Lands in Transition,” Publication 90 (Washington, D. C.: AAAS, 1970).
3. Jeremy A. Sabloff, in “Patient Earth,” ed. by John Harte and Robert Socolow (New York: Holt, Reinhart & Winston, 1971), pp. 16–27.
4. Allen H. Barton, “Communities in Disaster: A Sociological Analysis of Collective Stress Situations” (New York: Doubleday, 1969), p. 20.