MLA
Slagle, Bear. Letter from Bear Slagle (Atlanta, Georgia) to "Dear Uncle." Slagle Talks of the Atlanta Campaign and the Working of the Draft - September 12, 1864 (Photocopy). 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 20, Folder 24. https://digital.library.emory.edu/purl/501pg4f5x6-cor.
APA, 6th edition
Slagle, B. (1864). Letter from Bear Slagle (Atlanta, Georgia) to "Dear Uncle." Slagle talks of the Atlanta Campaign and the working of the draft - September 12, 1864 (photocopy) (Box 20, Folder 24) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/501pg4f5x6-cor.
Chicago
Slagle, Bear. “Letter from Bear Slagle (Atlanta, Georgia) to ‘Dear Uncle." Slagle Talks of the Atlanta Campaign and the Working of the Draft - September 12, 1864 (Photocopy).” Letters (correspondence). Civil War Collection, 1864. Box 20, Folder 24. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/501pg4f5x6-cor.