At about half a mile’s distance to the southward, there is another stone called the Buck Stone, upon which the proprietor of the barony of Pennycuik is bound by his charter, to place himself, and to wind three blasts of a horn, when the king shall visit the Borough Moor.
From p90 of Black’s Picturesque Tourist of Scotland By Adam and Charles Black (1861). Viewable online at Google Books.