The History of Middle-earth
The Cirth is not the only runic writing system used by Tolkien in his "legendarium". In fact, he devised a great number of runic alphabets, of which only a few others have been published. Some of these are included in the "Appendix on Runes" of "The Treason of Isengard" ("The History of Middle-earth", vol. VII), edited by Christopher Tolkien.