 Like pop music, lyrics often stress romantic love but also address a wide variety of other themes that are frequently social or political.By the late 1960s "classic rock" period, a number of distinct rock music subgenres had emerged, including hybrids like blues rock, folk rock, country rock, southern rock, raga rock, and jazz rock, many of which contributed to the development of psychedelic rock, which was influenced by the countercultural psychedelic and hippie scene.New genres that emerged included progressive rock, which extended the artistic elements, glam rock, which highlighted showmanship and visual style, and the diverse and enduring subgenre of heavy metal, which emphasized volume, power, and speed.