MLA
Guyler[?], Rich M. Letter from Ordnance Officer Rich M. Guyler[?] to Confederate Major General Leonidas Polk - October 18, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 6, Folder 57. https://digital.library.emory.edu/purl/767wm37qkd-cor.
APA, 6th edition
Guyler[?], R. M. (1861). Letter from Ordnance Officer Rich M. Guyler[?] to Confederate Major General Leonidas Polk - October 18, 1861 (Box 6, Folder 57) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/767wm37qkd-cor.
Chicago
Guyler[?], Rich M. “Letter from Ordnance Officer Rich M. Guyler[?] to Confederate Major General Leonidas Polk - October 18, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 6, Folder 57. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/767wm37qkd-cor.