According to Tommy Jarrell, he & his brother-in-law learned it from Jim Rawley (1900-82)
and they played it in the key of A
(the same as Fields Ward play it in, but I'm not counting in any capoes/lower pitch).

Later on Jarrell switched fiddle tuning to dDAD (low to high), thereby changing his version to the key of D.   

It is on his record, 'Sail Away Ladies' (County), titled 'Raleigh And Spencer',
although he apparently also called it 'Ryland Spencer'
(Brad Leftwich's Old-Time Fiddle book, sub: tunes learned directly from Tommy Jarrell; my edit)

Regarding Field's version of the song:
Paul Brown, who used to play with Fields Ward in his later years, said
Fields learned the song from black railroad workers.

Fields & Wade Ward has the tune here:

https://www.youtube.com/watch?v=Xeq7Y82iDLk

(I don't expect that duet record will be reissued in any form,

unfortunately defunct labels seems to take their releases with them)