Ralph
Thanks indeed for the very helpful quote. Having posted my thread and switched the machine off, I turned to my pile of books wishing that I had not taken The Horn Book by Gerald Legman back to the Edinburgh University Library 10 days ago. Then I noticed the volume lying there, and remembered that although I took it to the library, the library was shut for internal work!
Legman says "Stephen Foster cribbed and copyrighted a Negro folksong in 1850, and collected royalties on it for years under the name of 'The Camptown Races'."
Mind you, that proves nothing - Legman often just plain wrong in The Horn Book. (But don't please tell him I said so - if he's still living he must be more ferocious even than he is in the book.)
Thanks again
Ewan