Almost all early seventies hard rockers were firmly rock'n'roll entrenched, Purple (Gillan was an Elvis and Little Richard nut - and you can hear it too), Uriah Heep, Sabbath, UFO etc. Zep was the one exception with their Blues focus. Blues might have been the grandfather of hard rock, but rock'n'roll was its daddy. That is a small wonder given that both types of music addressed the same ethnic age and gender group: adolescent male whites with aggression to burn (and no girlfriends yet!).