Cranky Yankee,
Do you have any other snatches of the song? I did a quick search, and the only song I've come up with in the DigiTrad that mentions the Murray (as a river and not an earl!) is "Gumtree Canoe." It might help to have some other points of reference, especially a line or two; the opening line of the song can be very helpful, in case someone has it in a book but by a different title.
Sarah