There is some discussion of the exchange in "Columbus Georgia 1865," by Charles A. Misulia, University of Alabama Press, 2010. Apparently in early 1865 CS generals Howell Cobb, D.H. Maury and Gideon Pillow undertook to relieve themselves of some of the burden imposed by Union POWs at Andersonville. In March 1865, these men successfully moved 1,500 prisoners from Andersonville to Jackson, Mississippi, and turned them over to Union authorities. That success led to another effort in March 1865 to move prisoners from Andersonvile by rail to Columbus, GA; then down the Chattahooche River to near Quincy; and from there by rail to Jacksonville -- just a short march from Union-held St. Augustine. Howell Cobb appoined his aide, Col. Charles A.L. Lamar, to oversee the effort. Under the guard of three regiments of the Georgia Reserve Force, 6,000 prisoners were moved to Jacksonville.