Associated with shape note singing - a type of music that began in the American Northeast and spread to a few other similar traditions. We used to sing pieces in a folk music society. It is terrific fun for those of us with poor voices as it is primal and often sung at full throttle.
Listening to a piece on Ingram Marshall I caught a nice bit starting around the 38 minute mark.
(not terribly happy in all browsers - try the link if the embed doesn't work)