There are twenty duns, or ancient forts, in Tiree, it is said, but I have only seen eight, and examined two [..]. These duns, in the popular imagination, are all connected with Ossian's heroes, and I have had some difficulty in convincing the people that I am not in search of gold. There is a rhyme which says that Fionn left his gold in Dun Shiatar, which is situated near Hynish.
Ancient Sculpturings In Tiree. By Ludovic Maclellan Mann. From the Proceedings of the Society of Antiquaries of Scotland, Vol. 56
February 13, 1922.
The article mentions (with illustrations) cup marked stones at Gott Bay, Cornaigmore, Cuigeas, including some on a Standing-stone at Balinoe and others on the natural rock surface of floor of Kirkapoll Chapel.
Clach a'Choire (Cup and Ring Marks / Rock Art) — Folklore
This huge granite(?) boulder is covered (except underneath) with cup marks. It's known as 'The Ringing Stone' because if you strike it with a pebble it resonates with a metallic noise. People say that if the stone is ever broken, or falls off its platform of little stones, Tiree will sink beneath the sea. So let's not hit it too hard then, just in case. Unless you're good at swimming.