Yes - for a short section of that frontier.
It was the border between Pennsylvania (free soil) and slave-owning Maryland.
Mason Dixon Line
Maryland (slave) and Pennsylvania (free soil).
The Mason-Dixon line
Mason Dixon line
Maryland (slave) and Pennsylvania (free soil)
mason Dixon line
Mason and Dixon surveyed the border between Maryland and Penn's domain of Pennsylvania and Delaware State. This tour follows the southern border of Pennsylvania covered bridges in Pennsylvania, Delaware and Maryland. This is a tour of covered bridges, not of the Mason-Dixon line
Maryland (slave) and Pennsylvania (free soil)
The Mason-Dixon line.
It separated Pennsylvania (free soil) from Maryland (slave). Maryland did not join the Confederacy, so it remained a Union state.
Slave country from free soil.
No. It was free soil. Its border with slave-owning Maryland was the famous Mason-Dixon line.