Mason and Dixon's Line, so called after English engineers who surveyed it 1764-67; is the boundary separating Maryland from Pennsylvania and Delaware; during the Civil War it was inaccurately regarded as dividing the slave-holding from the free States, Maryland and Delaware both recognising slavery.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Mason, William * Maspero, Gaston Camille Charles