I first heard A bog down in the valley oh sung by Brian Kelly, a fellow member of Idle Fellows, in 1989 and it was love at first hearing. It is a wonderful accumulative song which goes on and on and on. It takes a lot of practice and is a real strain on the memory especially if you're playing and instrument at the same time. I sing it at practically every performance and it always goes down well. On two occasions I've had the great good fortune to sing it in duet with Victor Besch, a very good Welsh singer and musician living here in Bremen. He lets me rattle along, himself singing a blinding third above or below, on the fly and in perfect harmony. A most wonderful experience. His version includes a further verse about a leaf which in the heat of the moment, I leave out irregularly, but he takes it with aplomb.
I've also heard a Bavarian version, sung by Egbert Heiß, to a completely different tune. It is delightfully comic, especially the way Egbert sings it, and is completely in accord with the English version.
Recently (October, 2013), I found another amusing variant under the title of The Everlasting Circle given in Marrow Bones. Interestingly it has the feather -> bed -> maid -> man -> seed sequence which I find particularly droll.

Lyrics