From The Glenriddell MS., quoted in The English and Scottish Popular Ballads vol. I, F.J. Child, 1884:

"Carterhaugh is a plain at the confluence of the Ettrick with the Yarrow, scarcely an English mile above the town of Selkirk, and on this plain they show two or three rings on the ground, where, they say, the stands of milk and water stood, and upon which grass never grows."