 The Pretty Things' "SF Sorrow" (1968), and the Kinks' "Arthur (Or the Decline and Fall of the British Empire)" (1969) introduced the format of rock operas and opened the door to concept albums, often telling an epic story or tackling a grand overarching theme.King Crimson's 1969 début album, "In the Court of the Crimson King", which mixed powerful guitar riffs and mellotron, with jazz and symphonic music, is often taken as the key recording in progressive rock, helping the widespread adoption of the genre in the early 1970s among existing blues-rock and psychedelic bands, as well as newly formed acts.The vibrant Canterbury scene saw acts following Soft Machine from psychedelia, through jazz influences, toward more expansive hard rock, including Caravan, Hatfield and the North, Gong, and National Health.