Originally the music of the black rural population of the South American states, originating from negro spirituals and slave songs. Around 1900 this gave rise to the country blues: simple lamentations with acoustic guitar or piano accompaniment. When the poor blacks escape the racism and unemployment of the south, they also take their blues with them to the north. Muddy Waters is one of the first artists to amplify the blues electrically. In this 'Chicago blues' the line-up crystallises as well, which later becomes essential in pop music: vocals, guitar, bass guitar and drums. In several American cities blues scenes arise, each with a unique sound. An essential pop variant is the white blues or blues rock, which appeared in England in the sixties. Groups like Led Zeppelin and The Rolling Stones make good graces with text and music that they sometimes literally 'borrowed' from their older, black examples.