There's a "Mother Goose" rhyme very much like this, about a woman trying to get a pig home from market, but my mother goose books are out of reach at the mo'... I'll post tomorrow.

I also wonder why the sea would have coals... seems like the last place you'd go for such a request. Perhaps this song was translated into from another language, and it went funky somewhere along the way [That's how Cinderella's slippers went from being made out of squirrel skin to being glass]