Here's some verses to "Sheep Shell Corn" from Thomas Talley's NEGRO FOLK RHYMES, 1922:

http://books.google.com/books?id=C6YqAAAAMAAJ&pg=PA59&dq=sheep+shell+corn&cd=2#v=onepage&q=sheep%20shell%20corn&f=false

And the tune from Brown, mentioned above by Lighter:

http://books.google.com/books?id=sKlOYEg_5c8C&pg=PA135&dq=Sheep+shell+corn&cd=3#v=onepage&q=Sheep%20shell%20corn&f=false

I've always liked this little rhyme and I think it would make a fine chanty, being the lubber that I am.