conceptual, abstract, or based in fantasy and science fiction. 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. Greater commercial success was enjoyed by Pink Floyd, who also moved away from psychedelia after the departure of Syd Barrett in 1968, with The Dark Side of the Moon (1973), seen as a masterpiece of the genre, becoming one of the best-selling albums of all time. There was an emphasis on instrumental virtuosity, with Yes showcasing the skills of both guitarist Steve Howe and keyboard player Rick Wakeman, while Emerson, Lake & Palmer were a supergroup who produced some of the genre's most technically demanding work. Jethro Tull and Genesis both pursued very different, but distinctly English, brands of music. Renaissance, formed in 1969 by ex-Yardbirds Jim McCarty and Keith Relf, evolved into a high-concept band featuring the three-octave voice of Annie Haslam. Most British bands depended on a relatively small cult following, but a handful, including Pink Floyd, Genesis, and Jethro Tull, managed to produce top ten singles at home and break the American market. The American brand of progressive rock varied from the eclectic and innovative Frank Zappa, Captain Beefheart and Blood, Sweat & Tears, to more pop rock orientated bands like Boston, Foreigner, Kansas, Journey, and Styx. These, beside British bands Supertramp and ELO, all demonstrated a prog rock influence and while ranking among the most commercially successful acts of the 1970s, heralding the era of pomp or arena rock, which would last until the costs of complex shows (often with theatrical staging and special effects), would be replaced by more economical rock festivals as major live venues in the 1990s. The instrumental strand of the genre resulted