MLA
Huntingdon, Selina Hastings, Countess of, 1707-1791. Letter from Selina Hastings Huntingdon to Miss HIll, December 10. between 1707 and 1791. Selina Hastings Letters, 1774-1791, undated. Pitts Theology Library. https://digital.library.emory.edu/purl/4644qrfjrk-cor.
APA, 6th edition
Huntingdon, Selina Hastings, Countess of, 1707-1791. (between 1707 and 1791)[Letter from Selina Hastings Huntingdon to Miss HIll, December 10]. Selina Hastings Letters, 1774-1791, undated, Pitts Theology Library. https://digital.library.emory.edu/purl/4644qrfjrk-cor.
Chicago
Huntingdon, Selina Hastings, Countess of, 1707-1791, Letter from Selina Hastings Huntingdon to Miss HIll, December 10, between 1707 and 1791, Selina Hastings Letters, 1774-1791, undated, Pitts Theology Library. https://digital.library.emory.edu/purl/4644qrfjrk-cor.