MLA
Boyd, W. S. Letter from W. S. Boyd (Williamsburg, Virginia) to Confederate General Wilmot Gibbes De Saussure Asking Him to Arrange for Him to Go by Railroad to Pick His Daughters up from School in Columbia, South Carolina - June 3, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 3, Folder 3. https://digital.library.emory.edu/purl/11615dv546-cor.
APA, 6th edition
Boyd, W. S. (1864). Letter from W. S. Boyd (Williamsburg, Virginia) to Confederate General Wilmot Gibbes De Saussure asking him to arrange for him to go by railroad to pick his daughters up from school in Columbia, South Carolina - June 3, 1864 (Box 3, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/11615dv546-cor.
Chicago
Boyd, W. S. “Letter from W. S. Boyd (Williamsburg, Virginia) to Confederate General Wilmot Gibbes De Saussure Asking Him to Arrange for Him to Go by Railroad to Pick His Daughters up from School in Columbia, South Carolina - June 3, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 3, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/11615dv546-cor.