Reddit mentions of Escaping the Delta: Robert Johnson and the Invention of the Blues

OK, I'll Start

B.B. King Blues All Around Me

Muddy Waters Can't be Satisfied

Robert Palmer Deep Blues

Alan Lomax Land Where the Blues Began

Robert Johnson Escaping the Delta

The most obvious thing to say is that it isn't "written" at all. It's a kind of folk music, handed down by ear. Before audio recording it would have been learned from older musicians in person; after audio recording it could have been learned that way, at least in part.

Before audio recording there would have been natural geographical variations in style. Most blues musicians were "songsters", generally itinerant, travelling around picking up songs and entertaining, but many would have stayed more local. There was a lot of overlap between blues, folk, parlour songs, vaudeville, ragtime, etc. Performers sang and played anything that appealed to their audiences. It was only when blues suddenly became fashionable in the 1920s as the new record companies discovered how well it sold, that performers were asked to focus on blues tunes when recording. No ragtime or vaudeville comedy numbers please....

In terms of guitar technique, the piedmont style probably arose from banjo techniques, but perhaps also a way of imitating ragtime piano. The Delta style - often in open tuning with slide - had seemingly more influence from the parlour tunes of Henry Worrall (whose tune "Sebastopol" lent its name to open D tuning) and Hawaiian "slack key" guitar. Naturally there was overlap. Mississippi John Hurt, for example, straddles both styles.

The wiki pages on delta and piedmont styles reference some books: https://en.wikipedia.org/wiki/Piedmont_blues - https://en.wikipedia.org/wiki/Delta_blues. I don't know those myself, but a good book on various blues myths is Elijah Wald's Escaping the Delta. Guitarist John Fahey wrote an excellent monograph on Charley Patton, dealing with both blues history and Patton's style and technique.

EDIT: a full PDF of the Fahey book (highly recommended if you want PhD detail) can be found here.

Good time to ask this as I've just finished Escaping the Delta. It talks about the creation of blues in general and has a heavy focus on Robert in some chapters. Very good read!

http://www.amazon.com/gp/aw/d/0060524278?pc_redir=1407876148&robot_redir=1