MLA
Erskine, Anne Agnes, Lady, 1739-1804, Huntingdon, Selina Hastings, Countess of, 1707-1791. Letter from Selina Hastings Huntingdon to "My dearest madam" Hill, College, South Wales, May 19, 1774. May 19, 1774. Selina Hastings Letters, 1774-1791, undated. Pitts Theology Library. https://digital.library.emory.edu/purl/122v41nsjd-cor.
APA, 6th edition
Erskine, Anne Agnes, Lady, 1739-1804, & Huntingdon, Selina Hastings, Countess of, 1707-1791. (May 19, 1774)[Letter from Selina Hastings Huntingdon to "My dearest madam" Hill, College, South Wales, May 19, 1774]. Selina Hastings Letters, 1774-1791, undated, Pitts Theology Library. https://digital.library.emory.edu/purl/122v41nsjd-cor.
Chicago
Erskine, Anne Agnes, Lady, 1739-1804, Huntingdon, Selina Hastings, Countess of, 1707-1791, Letter from Selina Hastings Huntingdon to "My dearest madam" Hill, College, South Wales, May 19, 1774, May 19, 1774, Selina Hastings Letters, 1774-1791, undated, Pitts Theology Library. https://digital.library.emory.edu/purl/122v41nsjd-cor.