What is the theme in Mystery Train: Images of America in Rock 'n' Roll Music by Greil Marcus?

Racism is a theme through the book. Throughout his criticism Marcus, indicates there were a variety of racial issues associated with the creation of rock 'n' roll music. Rock 'n' roll music seems to have stemmed from blues music, a form of music made popular by blacks. In his chapter about Harmonica Frank, Marcus writes how Sam Phillips hopes to find a white singer with a black sound.