MLA
Floyd, William L. Letter from William L. Floyd (Folly Island, near Charleston, South Carolina) to Rufus Heywood. Floyd Was Chaplain of the 112th New York Infantry Regiment; the Letter Informs Heywood of the Death of Corporal Frank Bullock - August 31, 1863. 1863. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 19, Folder 23. https://digital.library.emory.edu/purl/194hmgqppz-cor.
APA, 6th edition
Floyd, W. L. (1863). Letter from William L. Floyd (Folly Island, near Charleston, South Carolina) to Rufus Heywood. Floyd was chaplain of the 112th New York Infantry Regiment; the letter informs Heywood of the death of Corporal Frank Bullock - August 31, 1863 (Box 19, Folder 23) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/194hmgqppz-cor.
Chicago
Floyd, William L. “Letter from William L. Floyd (Folly Island, near Charleston, South Carolina) to Rufus Heywood. Floyd Was Chaplain of the 112th New York Infantry Regiment; the Letter Informs Heywood of the Death of Corporal Frank Bullock - August 31, 1863.” Letters (correspondence). Civil War Collection, 1863. Box 19, Folder 23. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/194hmgqppz-cor.