How does Greil Marcus use imagery in Mystery Train: Images of America in Rock 'n' Roll Music?

Imagery:

"They sang as if they knew they were destined to survive not only a few weeks on the charts but to make history; to displace the dreary events of the fifties in the memories of those who heard their records; and to anchor a music that twenty years later would be struggling to keep the promises they made. Naturally, they sound as if they could care less, so long as their little black 45's hit number one and made them rich and famous. But they delivered a new version of America with their music, and more people than anyone can count are still trying to figure out how to live in it."

"A musical vacuum was opening up, and the racial contradictions of the counterculture were coming to the surface. There was no music to work out the contradictions, and no music to fill the vacuum."