References for Sir William 3rd Baron, Marquess Herbert * Powis * of Powis

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Sir B.Burke: A Genealogical History of the Peerages and Knightages of the British Empire. London, 1953
Sir B.Burke: Burke's Peerage and Baronetage. London, 1999
F.M.Powicke, E.B.Fryde: Handbook of British Chronology. London, 1961