W. J. CASH: A Life by Bruce Clayton (Louisiana State University Press: $24.95; 236 pp.). Wilbur Joseph Cash (1900-1941) wrote exactly one book, but what a book: "The Mind of the South," the critical exploration of the Southern temperament, first published 50 years ago and continuously in print ever since. Cash was a true son of the South, rarely venturing beyond the Carolinas, and Allegheny College professor Bruce Clayton does a good job sketching the love/hate ambivalence that drove Cash to write his classic--and, one suspects, to suicide. Cash hanged himself in Mexico City in 1941, the same year "The Mind of the South" was published, and although Clayton leans toward a physiological explanation of Cash's suicide--deep depression caused by hyperthyroidism--his evidence probably will lead many readers to conclude that Cash ended his life because he knew, at some level, that his only significant work was behind him.