1. forest region. Bull. 18. Nacogdoches, Texas: School of Forestry, Stephen F. Austin State University, 1969.
2. Atwood, W.W. The physiographic provinces of North America. Ginn Co., New York, 1940; and Fenneman, M.M. Physiography of the Eastern United States, McGraw-Hill Book Co., New York, 1938.