The author contends that the island of Britain was the seat of the development of a cultus and secret tradition of extraordinary vitality and individuality. In this volume he has collected data concerning it and made an effort to systematize it. Contents include: Cult of the Dead; The Mystery of Celtic Philosophy; _Barddas_; The Arcane Tradition in British Mediaeval Literature; The Mystery of the Grail; The Secret Tradition in Rite and Legend; The Higher Philosophy of British Mysticism; The Way of Initiation; The Writings of _Morien_; Druidism and the Secret Tradition in Ireland.