A while back, I was sorting and tagging mp3s as the CD player over my left shoulder ran through the two-disc set Night Train to Nashville , subtitled “Music City Rhythm & Blues, 1945-1970.” Deep into the second disc of the set borrowed from the local library, I’d already heard a lot of stuff I wished I’d heard long ago, much of it on the Excello label. A new track began: a thrumming bass with two measures of eighth notes solo, then percussion on the backbeat for two more measures. And then: “Doooo, do-do doo. Do-do-do! Do-do-do! Do-do-do.” I jerked my head around, stared at the CD player as the verse began: “Dancin’ with you, baby, really turns the soulshake on. Yeah, groovin’ with you, baby, really turns the soulshake on.” Knowing the song as “Soul Shake” but never having heard this version, I reached for the booklet that came with the set. The track was by Peggy Scott and Jo Jo Benson, recorded in Nashville in 1969 and released as “Soulshake” early that yea...