Check out this cool-ass 1990 interview with Ry Cooder by Jas Obrecht. The talk is Blind Willie Johnson and the Blues:
Q: What’s your attraction to “Dark Was the Ground – Cold Was the Night”?
RC: That’s the most transcendent piece in all American music, the way he used his voice and the guitar. This other tune that I love so much is “God Moves on the Water.” Oh, that thing is like a roller coaster, man. He’s got an energy wave in there that he’s surfing across the face of that tune so mighty! He hits the chorus, and to me it’s like ice skating or downhill racing – it’s an awesome physical thing that happens. But “Dark Was the Night” is the cut – everybody knows that lick. You can throw that lick at anybody nowadays. I threw it up inside Paris, Texas, you know, and everybody relates. And now you play that lick, and everybody knows what it is. It’s like an unspoken word. It’s really amazing. [Legally download these tracks at http://www.archive.org/.]
I’ll really tell you, Blind Willie Johnson is in the ether somewhere. He’s up there in the zone somewhere. But if he played flat . . . And at this point, after talking with you, I’m starting to feel that really would account for it. Because I know that if it was regular, I could be doing it. I can do what he did – I can play those notes now. I mean, I have learned. My co-ordination and understanding have developed to the point where I am capable of executing those passages, but it sounds really different when you play flat.
Here’s Cooder’s version.