MLA
Seddon, James A. Letter from James A. Seddon to James Longstreet (New Orleans, Louisiana) - May 3, 1875 (Typescript). 1875. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 4, Folder 50. https://digital.library.emory.edu/purl/6214mw6n9r-cor.
APA, 6th edition
Seddon, J. A. (1875). Letter from James A. Seddon to James Longstreet (New Orleans, Louisiana) - May 3, 1875 (typescript) (Box 4, Folder 50) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6214mw6n9r-cor.
Chicago
Seddon, James A. “Letter from James A. Seddon to James Longstreet (New Orleans, Louisiana) - May 3, 1875 (Typescript).” Letters (correspondence). Civil War Collection, 1875. Box 4, Folder 50. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6214mw6n9r-cor.