Song of Yste - a book of “preglacial” origin (Thulean? — it was known to the antehumans of Thule according to the Book of Eibon ) which was translated in mediaeval times into Greek, Latin, Arabic and Middle English by the Dirkas Monks. It may have taken the form of a classical epic poem (it is compared to the Hindu epic poems), although the poetry has been lost in translation and it is now a rather dull, heavy read. It seems to mention the antehuman land of Arkya.
The Song of Yste was created by Rober A. W. Lowndes, and expanded on by Lin Carter and Laurence J. Cornford.