The quote below places the tune "The Martyrs" to before 1679.

The Laird of Torfoot in an article which he penned when he returned from exile and from it I condense. "It was," says the Laird, "a fair Sabbath morning, 1st June. A.D. 1679, that an assembly of Covenanters sat down on the healthy mountains of Drumclog. All being in readiness, the women and children, and the old men, with their bonnets in their hands, and their long grey locks streaming in the wind, retired to a convenient distance, fervently singing a psalm to the tune of "The Martyrs"

In another book. Men of the Covenant, ".....Down the face of the slope the Covenanters advanced, singing the familiar verses of one of the Scottish metrical psalms, the 76th, to the fine old tune of "Martyrs".

In Judah's land, God is well known
His name's in Israel great;
In Salem is his tabernacle.
In Sion is his seat.
There arrows of his bow He break
The shield, the sword, the war,
More glorious Thou than hills of prey,
More excellent are by far. (etc.)

The meter fits Amazing Grace and could this be the same tune (or related to) the "Martyrdom" written by Hugh Wilson in 1800 which is obviously closely related to the tune known as Amazing Grace?