Dovefeather:
I second the "looks like it might be" comment of Old Dog. According to my reference, Olgam-language messages were sometimes written with consonants only. That middle line referred to as the base of the writing separated the consonants and vowels. Consonants on one side and vowels to the other. Also, the writing was usually written vertically. That means; those marks would be drawn horizontally in relation to the ground with the base dividing line running vertically. Your stone carving looks like it could be a combination of consonants only and some words with consonants AND vowels. By these guidelines, your stone is laying on it's side.