MLA
[unknown]. Letter from [unknown] (Peterborough, New Hampshire) to "Dear Brother," [who supported the Confederacy] regarding Peterborough's contribution to the war effort - December 22, 1865. December 22, 1865. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/552w3r23bj-cor.
APA, 6th edition
[unknown]. (December 22, 1865)[Letter from [unknown] (Peterborough, New Hampshire) to "Dear Brother," [who supported the Confederacy] regarding Peterborough's contribution to the war effort - December 22, 1865]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/552w3r23bj-cor.
Chicago
[unknown], Letter from [unknown] (Peterborough, New Hampshire) to "Dear Brother," [who supported the Confederacy] regarding Peterborough's contribution to the war effort - December 22, 1865, December 22, 1865, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/552w3r23bj-cor.