Dunadd, and Cup Shaped Depressions

First, a closeup of Dunadd's "cup":

South of Kilmartin Valley, and of the Crinan Canal there is a township (now a B&B, White Rock Bed and Breakfast), known by the Gaelic name "Leacnabaan". Mr Hamilton, the proprietor, is an enthusiastic historian (as is his wife), and he has noticed several things about this place. When he looks north through a notch in the hills, Dunadd is clearly in sight. In fact, he believes that a small rise next to his home would have been ideal for placing signal fires (ie, like in the Lord of the Rings movie).

And then, close to a fallen standing stone at Leacnabaan, there is ANOTHER cup shaped depression:

Finally, there is a very similar cup shape inside St Columba's Cave on Loch Caolisport!

Interesting, No?? If anyone has archaeological/historical notes relating to these 'cups', let me know.