Howdy,
According to the Joan Baez songbook from 1964, Joan plays in Em with a capo at the first fret to sing in Fm.
As [Em] I walked [D] out over [C] London [Em or G] Bridge [Em]
One misty [Em or G] morning [D] early,
[Em] I over- [Em or G] heard a [D] fair pretty [Bm] maid
[C] Was la- [G] menting [B7] for her [Em] Geordie.
Hope it helps.
Allinkausay, Bill