12Price, Liam. "Glencolumbkille, County Donegal, and Its Early Christian Cross-Slabs." The Journal of the Royal Society of Antiquaries of Ireland Seventh 11.3 (1941): 74.
On p. 55, the author quotes John Ewing (Statistical Return of Glencolumbkille, 1823:2): "There is a stone of very particular use in curing head aches which must be lodged every night in St Columb's bed but is generally taken off every morning through the parish. I was not fortunate enough to see it tho' I called twice—but each time it was out on duty."