William Mahone died on October 8, 1895, so it must have been one of the last things he wrote. I didn't find anything on the subject of Burgess' Mill and Hatcher's Run in the Southern Historical Papers or in the "Battles and leaders of the Civil War" series." I have copies of Mahone's articles in the "Historical Magazine" (1871) and some correspondence with Longstreet and Wilcox from the files at the Library of Virginia. I also have copies of several papers and presentations about William Mahone, but their bibliographies show nothing he authored with a date of 1895. I know the Perkins Library at Duke has "The William Mahone Papers," but I did not see a reference there to the above-mentioned battles.