I have recently been considering a theory I have, that the writing on the ancient Gala graves and monuments of northern Somalia is an archaic, pre-Islamic dialect of Somali, written in South Arabian, an alphabet used in Yemen and Ethiopia from 600 BC to about 600 AD.
My theory is that the Yibir kingdom of Hargeisa of oral history and the Gala civilization are one and the same, and that they spoke the Yibir dialect of Somali (an archaic form) and wrote their dialect in South Arabian, due to their links to Yemen from a millenia of the incense trade.
If you know of any Gala writing on old rocks or monuments, I've put together a South Arabian to Somali transliteration key, if anyone is interested. Hopefully someday I can try to discover the lost cities of Mosyllon and Mundus.
http://upload.wikimedia.org/wikipedia/c ... somali.gif
Let me know if it works! I know there are lots of Gala sites especially near Hargeisa and in Sanaag.