MLA
Pettus, John Jones, 1813-1867. Letter with official state seal affixed, from John J. Pettus, Governor of Mississippi, addressed to the Governor of Georgia, Joseph E. Brown, instructing him that the State of Mississippi will be sending a commissioner, Theo W. White, to the State of Georgia announcing the secession of Mississippi, and hoping that Georgia will assist and join with Mississippi - November 30, 1860. November 30, 1860. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/791sf7m1qx-cor.
APA, 6th edition
Pettus, John Jones, 1813-1867. (November 30, 1860)[Letter with official state seal affixed, from John J. Pettus, Governor of Mississippi, addressed to the Governor of Georgia, Joseph E. Brown, instructing him that the State of Mississippi will be sending a commissioner, Theo W. White, to the State of Georgia announcing the secession of Mississippi, and hoping that Georgia will assist and join with Mississippi - November 30, 1860]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/791sf7m1qx-cor.
Chicago
Pettus, John Jones, 1813-1867, Letter with official state seal affixed, from John J. Pettus, Governor of Mississippi, addressed to the Governor of Georgia, Joseph E. Brown, instructing him that the State of Mississippi will be sending a commissioner, Theo W. White, to the State of Georgia announcing the secession of Mississippi, and hoping that Georgia will assist and join with Mississippi - November 30, 1860, November 30, 1860, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/791sf7m1qx-cor.