Just listening to the ultra-legendary Robert Johnson’s recordings:
What else should I be keeping my ear out for pre-1950 that would help educate me about what influenced rock n roll music? You HAVE TO MAKE A CASE FOR IT. (IE Robert Johnsons “Crossroads” was covered by Cream, and one of their most memorable hits ever).
Sister Rosetta Tharp, “Strange Things Happening Everyday” from 1944.
She influenced everyone from Little Richard to Rod Stewart.
The main lady seems pretty wacky. I suspect she’d have been into punk music, if she’d been born 50 years later.
Yeah, heaven forbid you hear any music from before 1950 that has nothing to do with rock. You don’t want to turn into that icky dude from Ghost World.
Jimmy Rodgers influenced a lot of blues musicians, which influenced rock.
Memphis Minnie was a big influence and one of the few blues artists Led Zeppelin credited without a lawsuit.
Not music, but you might want to read Chapter 19 of Sir Peter Hall’s Cities in Civilization which goes in detail about the development of rock and roll in the Mississippi Delta region. You can read a summary of the chapter in pages 13-15 of the following PDF: Here
Was the discussion ever agreed upon that Johnson was recorded slower than 78 RPM, giving a higher frequency to his voice?
Boogie woogie songs such as “Roll 'Em” by Meade Lux Lewis had an influence.
My favorite example, and my absolute favorite pre-1940 guitarist, is Blind Willie Johnson. Led Zeppelin recorded Nobody’s Fault But Mine. He also did other rockers, such as In My Time of Dying/ Jesus Make Up My Dying Bed, God Moves on the Water, and Soul of a Man.
Johnson also did the eeriest recording ever, Dark Was the Night, Cold was the Ground. It never fails to affect me.
Johnson was blinded by his stepmother with acid. His Father left him on the street to beg by playing. He considered himself to be a gospel singer. He died of exposure in his burned home, covered with wet newspaper because his Wife could not get a White hospital to take him in. His Wife is on one of his recordings.
She’s actually on more than one. She’s on Soul of a Man, and on John the Revelator, at least.
Muddy Waters and John Lee Hookerare both legends of blues that pretty much formed the foundation of everything you have heard in Rock since about 1963. Every band that has played a rock song was either influenced by them or by someone who was influenced by them. Look at their catalogs and you will recognize most of their songs from being hit remakes for famous bands from the 60’s, 70’s and 80’s.
Louis Jordan was a 1940s bandleader who popularized a genre called “jump blues”, basically a fusion of blues and more danceable music like swing. Here’s where Chuck Berry “borrowed” the guitar intro to Johnny B. Goode from:
Louis Jordan And His Tympany Five - Ain’t That Just Like a Woman (1946)
Jordan was born in Brinkley, Arkansas. A guy who does a local music history radio program, Arkansongs, is nuts about him. You would thing he was Robert Johnson or something. 
Louis Jordan, Aint That Just Like a Woman (1946) simplifies the melody and piano chords, which was kind of the dividing line between “race music” and the earliest Rock n Roll a few years later.
Damn, she is pretty.
I recall years ago hearing a weird version of Loch Lomond on the radio in a jazz form:
maybe it was this one:
[Loch Lomond ~ Maxine Sullivan ~ 1937](http://boards.straightdope.com/sdmb/Loch Lomond ~ Maxine Sullivan ~ 1937)
In many cases, I find that older music was not always so distinct from what later came to be called Rock ‘n’ Roll. Much of Rock ‘n’ Roll involved updated versions of old Tin Pan Alley songs or other vocal jazz classics like Blue Moon or Heart and Soul. I’m not a musician, but I don’t hear much in the great hits of The Platters that would stand out if it had been released in the same era as the Ink Spots or Mills Brothers songs from which they clearly drew inspiration. Yet, they’re considered Rock ‘n’ Roll.
What’s known as Doo-wop, a sound which is often immediately recognized as belonging to the genre of 50’s Rock ‘n’ Roll, has clear origins in black vocal harmony groups of the 30’s and 40’s, and these themselves can be traced back to the barber shop quartets of what seems like an impossibly old timey era.
The old World War II anthem White Cliffs of Dover has been covered again and again under the umbrella of Rock ‘n’ Roll: The Five Keys, The Blue Jays, The Checkers (excellent lead bass), The Del Vikings, Lee Andrews & The Hearts, The Mystics, The Robins, The Willows. I’m sure I’m missing some.
The old Mills Brothers tune Gloria is largely remembered as a Doo Wop standard. It’s been covered by The Cleftones, the Five Thrills, The Chariots, The Excellents, Vito & the Salutations, Arthur Lee Maye & The Crowns, The Cadillacs, The Chapelaires, The Chariots, The Del-Lourds, The Escorts, The Fascinators, The Five Chances, The Gems, The Intruders, The Lovenotes, The Passions, The Hi-Lites, The Sheps, etc.
There are other examples, but suffice it to say that Rock ‘n’ Roll music mined the music of previous generations heavily.
There’s always Lucille Bogan’s “Shave 'Em Dry.” (No link since it’s pretty filthy). Mick Jagger lifted a few lyrics from it.
I don’t think of the songs mentioned as “eerie,” as much as a part of my life for decades.
Skip James with a Cream song: I’m So Glad" (1931) James was a better guitarist than Johnson, but so were a lot of people. When Johnson claimed the Devil was teaching him to play, his contemporaries thought instead that he had taken a year off to practice. Skip had practiced already.
James “Iron Head” Baker -or- Chain Gang meets Ram Jam: Black Betty (1933) John Hammond collected another old one, but I can’t find it. A woman sang it. Loud, fast, and stupid; real Rock & Roll.
Ma Rainey vs pretty much everybody: See See Rider (1925)
Big Joe Williams vs everybody else: Baby, Please Don’t Go (1935) Ted may be crazy, but he wins.
This is is fun! I could do it all night.