MLA
Carson, Thomas. Letter from Thomas Carson to Daniel Davis (Richmond, Virginia) - May 14, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 2, Folder 8. https://digital.library.emory.edu/purl/890rr4xhxh-cor.
APA, 6th edition
Carson, T. (1861). Letter from Thomas Carson to Daniel Davis (Richmond, Virginia) - May 14, 1861 (Box 2, Folder 8) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/890rr4xhxh-cor.
Chicago
Carson, Thomas. “Letter from Thomas Carson to Daniel Davis (Richmond, Virginia) - May 14, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 2, Folder 8. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/890rr4xhxh-cor.