Green’s Dictionary of Slang

1. (US) a native of Florida.

1826		T. Flint Recollections 319: [The people of W. Florida] are a wild race, but with little order or morals; they are generally denominated ‘Bogues,’ and call themselves ‘rosin heels.’.
1866		W. Reid After the War 416: ‘The rossum heels live in thar,’ a newsboy on the train informed me.
1983		Maledicta VII 28: Blacks also called poor whites rosin chewer, from an apparent practice of chewing, if not eating, pine rosin.

2. (US black, also rosum belly) a derog. term for a white peasant.

1927		‘Sawmill Talk’ AS III:1 24: The common laboror is variously known as ‘lumber rustler,’ ‘rosum belly,’ or ‘sawdust eater.’.
1981		L. Pederson LAGS Basic Materials [DARE].