From the Statistical Accounts (see link):
Antiquities. – Under this head, it may be mentioned, that, in a field a little to the west of the church, there is a singular upright stone, somewhat in the form of an obelisk, called Clach a Mhearlich, i.e. the thief’s stone, – which is evidently of very ancient date. Though in the midst of an arable field, it is most religiously preserved, no attempt being made to remove it, or alter its position. None even of the oldest inhabitants are acquainted with any distinct tradition, respecting its origin or intention; but, from the name, it is conjectured that some noted robber was buried beneath it.