This turf-covered stoney mound is, according to the scheduled monument record, very likely to be a Bronze age cairn. But Mr Miller has other ideas:
On the hill above Whitekirk, a cairn of stones marks the grave of two persons who were slain at a conventicle, by a party from the Bass. This was probably the meeting held here in May 1678, which was dispersed by Charles Maitland, deputy governor, when James Learmont and his brother, with one Temple, (from Dunbar) were pannelled, 11th September 1678, for the murder of John Hay, who came with the King's forces.
From p99 of James Miller's 1824 'St. Baldred of the Bass: A Pictish Legend.' Online at Google Books.