Lots of ideas I hadn't thought of. Thanks. I did wonder about Bartholemew for Black Bart's name but of course he was Charles E.
A load of girls is an interesting idea. And thanks Bob I did think I'd heard the term here in Australia. Foundry slang? Marijuana? Both worth a thought. You just never know.
The only small clue that I could add for what it's worth is that the performer Sam Cowell 1820-1864 who was raised in the American South always claimed to have written "Jim Along Josie". He probably didn't, but he is likely to have heard it during his childhood. He spent a lot of time among black musicians and also poor white ones. (his father was a poor entertainer and not a slave owner). It raises the possibility that "bart" is an African-American term.
Thanks again everyone. Perhaps I'm a bit closer.