In the '60s, Paul Butterfield mixed deep Chicago roots with a rock 'n' roll edge to create a trailblazing new sound in blues. You can catch his influence in The J. Geils Band's blend of dirty harmonica with biting guitar on the instrumental "Ice Breaker (For the Big 'M')," and in the way that Gary Clark Jr.'s "If Trouble Was Money" layers its darkened blues balladry with thick, crunched-up rock solos.