MLA
Marshall, Michael. Letter from Michael Marshall (Near Petersburg, Virginia) to His Mother, Mary Marshall. Michael Was a Solider in the United States Army, 17th Infantry Regiment, Company A and Died at the Battle of Globe Tavern in 1864 - August 3, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 23, Folder 20. https://digital.library.emory.edu/purl/955m905rtn-cor.
APA, 6th edition
Marshall, M. (1864). Letter from Michael Marshall (Near Petersburg, Virginia) to his mother, Mary Marshall. Michael was a solider in the United States Army, 17th Infantry Regiment, Company A and died at the Battle of Globe Tavern in 1864 - August 3, 1864 (Box 23, Folder 20) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/955m905rtn-cor.
Chicago
Marshall, Michael. “Letter from Michael Marshall (Near Petersburg, Virginia) to His Mother, Mary Marshall. Michael Was a Solider in the United States Army, 17th Infantry Regiment, Company A and Died at the Battle of Globe Tavern in 1864 - August 3, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 23, Folder 20. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/955m905rtn-cor.