 The song was tethered to a four-beat bass pattern and structured as a series of sections, each with a different mood, mode and color, always underscored by the drummer, who contributed not only the rhythmic feel but much in the way of tonal shading, using mallets as well as sticks on the various drums and the different regions of the cymbals.In addition to playing beautiful solos, Paul [Butterfield] played important, unifying things [on harmonica] in the background - chords, melodies, counterpoints, counter-rhythms.This was a group improvisation.