http://www.time.com/time/magazine/article/0,9171,1704683,00.html

The revival of a Christian four-part choral style called Sacred Harp (the name refers to the human voice and a songbook published in 1844). Once America’s dominant religious music, it was eclipsed after the Civil War. By 1960, say scholars, as few as 1,000 people clustered in the Deep South knew the style.