MLA
Smith, G. A. Letter from G. A. Smith to William E. Mickle - September 25, 1895. 1895. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 9, Folder 17. https://digital.library.emory.edu/purl/450gtht88j-cor.
APA, 6th edition
Smith, G. A. (1895). Letter from G. A. Smith to William E. Mickle - September 25, 1895 (Box 9, Folder 17) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/450gtht88j-cor.
Chicago
Smith, G. A. “Letter from G. A. Smith to William E. Mickle - September 25, 1895.” Letters (correspondence). Civil War Collection, 1895. Box 9, Folder 17. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/450gtht88j-cor.