What did Charles Mason and Jeremiah Dixon settled in the 1760s?

In the 1760s, Charles Mason and Jeremiah Dixon settled the boundaries between the British colonies of Pennsylvania and Maryland, famously demarcating the Mason-Dixon Line. Their work aimed to resolve long-standing territorial disputes between the two colonies. The line became significant not only for its geographical implications but also for its later symbolic association with the division between free and slave states in the United States.