For a manageable introduction to vintage roots music you could do much worse than Across the Tracks. In addition to covering the basics (old-time, country blues, hillbilly, rural gospel, string band, bluegrass, etc.), this collection crosses the color barrier. For example: Appalachian icons Clarence "Tom" Ashley and Bascom Lamar Lunsford rub shoulders with bluesmen Bukka White and Mississippi John Hurt. This is vital, as the history of American folk music is one of cross-pollination, not isolation.