MLA
Josh [last name unknown]. Letter from Josh [last name unknown] (Fort Pulaski, Georgia) to "Dear George" - March 28, 1862. March 28, 1862. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/081wdbrw24-cor.
APA, 6th edition
Josh [last name unknown]. (March 28, 1862)[Letter from Josh [last name unknown] (Fort Pulaski, Georgia) to "Dear George" - March 28, 1862]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/081wdbrw24-cor.
Chicago
Josh [last name unknown], Letter from Josh [last name unknown] (Fort Pulaski, Georgia) to "Dear George" - March 28, 1862, March 28, 1862, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/081wdbrw24-cor.