Teribus says: "Tune most commonly associated with the hymn is Scottish."

Are you sure? The name of the tune is "New Britain"! According to this page that Liland created – http://www.geocities.com/cigneto/thctxt/en/amazinggr2.html – "Despite its name, NEW BRITAIN appears to be a tune of American origin, first published and most widely attested in the fasola shapenote tradition of the second quarter of the 19th century, whence it migrated into mainstream hymnals in the twentieth century as the customary tune for 'Amazing Grace' ".