Edited by Robert Twombly, W.W. Norton, 2010, 344 pages, $25. Generally speaking, the writings of designers are not as important to understanding their intentions as their actual work. Frederick Law Olmsted’s copious writings are an exception, for two reasons. He was a man of letters before he was a landscape architect. He wrote The Cotton Kingdom, an influential chronicle of his travels as a newspaper correspondent in the ante-bellum South, edited Putnam’s Magazine, an important literary journal, and co-founded The Nation. Moreover, because he was not formally trained in an art or design school, Olmsterd approached park and landscape design