Bliss, if you look at where the main Bluegrass (and for that matter Country & Western) music developed, you will notice a pattern where a lot of the immigrants had been from Gaelic speaking areas of Scotland and Ireland. They brought the themes, and rhythms of their music and singing to America. The places they settled, along with English settlers for the most part, were places where the music was kept alive. Places such as the Appalachians, Virginia, the Tennessee region, North Carolina, and such all benefited by the waves of relatives coming after the original settlers. As they mingled with the Black settlers not only was the music changed, but some of the dancing was passed along. There seems to be a migrant path for the Step-dancing of Scotland and Ireland with the American Tap-dance and Clogging. Also, Irish/Scottish Set Dancing became the American Square Dance.