Tsath-Yo is the name given to the script used by the ancient Hyperboreans. It may also be their name for the Hyperborean language itself. It is made up of angular characters. The -ath suffix seems fairly prominent in Hyperborean nouns. A Mr. Garson Casterwell of Boston produced a monograph on the translation of Tsath-Yo towards the end of the Twenties. Entitled The Kranorian Annals, Fact or Fallacy? Only 1100 copies were printed.
Few original examples of Tsath-Yo have survived into the present day. Of those that did, the Book of Eibon is the most famous. St Azedarac of Ximes was rumoured to have held an original Hyperborean copy of the book in his collection. While it's unlikely an original copy would exist in bound book form there is always the possibility Azedarac possessed a reproduction of an original copy.
It is from Kranoira that we can gain many of our insights into the lives of the latter age Hyperboreans, so it is not surprising that several artefacts baring inscriptions in Tsath-Yo have also been unearthed there.