Celts or stone implements.---These in the west of Ireland, but especially in the Aran Isles, Galway Bay, are looked on with great superstition. They are supposed to be fairy darts or arrows, and are called saighead [syed] anglice dart. They had been thrown by fairies, either in fights among themselves or at a mortal man or beast. The finder of one should carefully put it in a hole in a wall or ditch. It should not be brought into a house or given to anyone, yet the Aranites are very fond of making votive offerings of them at the holy wells on the mainland. They carry them to the different patrons and leave them there; the reason for this I could not make out; they do not seem to leave them at the holy wells on the islands. A person supposed to be fairy-struck is said to have been "struck with a dart." Grown people who suddenly get fits are supposed to be struck with a saighead..
Notes on Irish Folk-Lore
G. H. Kinahan
The Folk-Lore Record, Vol. 4. (1881), pp. 96-125.
This isnt far from Kilronan and can be seen from the road as you head from Kilronan to Dun Aonghus. It is not as impressively situatied as Dun Aonghus but you actually get a better view of all parts of the island. Worth a look for the views alone.