MLA
Mashburn, Edward. Letter from Edward Mashburn to Henry Ward (Mount Mariah, Alabama). Edward Speaks of Visiting His Uncle in the Future and the Prices of Tobacco and Sugar Crops - August 16, 1845. 1845. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 14. https://digital.library.emory.edu/purl/6042rbp0tt-cor.
APA, 6th edition
Mashburn, E. (1845). Letter from Edward Mashburn to Henry Ward (Mount Mariah, Alabama). Edward speaks of visiting his uncle in the future and the prices of tobacco and sugar crops - August 16, 1845 (Box 5, Folder 14) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6042rbp0tt-cor.
Chicago
Mashburn, Edward. “Letter from Edward Mashburn to Henry Ward (Mount Mariah, Alabama). Edward Speaks of Visiting His Uncle in the Future and the Prices of Tobacco and Sugar Crops - August 16, 1845.” Letters (correspondence). Civil War Collection, 1845. Box 5, Folder 14. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/6042rbp0tt-cor.