I first heard this c. 1966/7 in my home town of Peebles in the Scottish Borders. We had "Saturday morning pictures" which some times featured live music, notably local beat group The Livewires. Sometimes we had a young lady folk singer who I think was involved with the Girl Guides. She used to sing "Rattling Bog" I always thought the "Rare bog, a rattling bog" meant a bog of some quality and distinction (by bog standards) She sang; In the valley was a bog, a rare bog a rattling bog and the bog's down in the valley o.
Then; In the bog there was a tree
And on the tree there was a branch
And on the branch there was a twig
And on the twig there was a leaf
And on the leaf there was a nest
And on the nest there was an egg
And on the egg there was a bird

Can't remember any more than that!

I think Bill Barclay did a ruder version which had the lines
On the bed there was a woman
And on the woman was a man
And on the man there was some sweat!

All this from memory.

Grahame Hood