The book is "Through the Valley of the Shadow of Death: The Civil War Manuscript Collection of Captain Harvey Alexander Wallace, 5th S.C. Infantry and 19th Texas Infantry, Walker's Texas Division", edited by Stephen R. Skelton. Wallace wrote a lot of letters home to his wife, and kept an interesting journal. The book came out not too long ago, so it should be available, or possibly your local library could find a copy for you.

One of the monuments at Fort DeRussy, dedicated to the 69 slaves who died while building the fort, has a quote by Wallace on the back of it, concerning how he would hide his slaves in the woods before he would ever have let any come work at the fort.