MASON AND DIXON'S LINE, the parallel of
lat. 39° 43' 26.3" N., which separates
Pennsylvania from Maryland, drawn by Charles
Mason and Jeremiah Dixon, two distinguished
English mathematicians and astronomers. As
the northern limit (with the exception of
small portions of Delaware and Virginia) of
the original slave states, it was prominently
mentioned in the controversies concerning
slavery. It begins at the N. E. corner of
Maryland, and runs due W. The years from
1681 to 1768 were marked with constant
dissension and conflict between the rival proprietaries
of Pennsylvania and Maryland and their
partisans, on the subject of their common
boundary; and the vicinity of this line was
the theatre of riot, invasion, and bloodshed. Mason and Dixon arrived in Philadelphia on Nov. 15, 1763, and commenced their work in December, which was continued to a point 244 m. from the Delaware river, and within 36 m. of the whole distance to be run, where they were compelled to suspend operations in consequence of opposition by the Indians. They returned to Philadelphia, and were discharged on Dec. 26, 1767. At the end of every fifth mile a stone was planted, graven with the arms of the Penn family on one side, and of Lord Baltimore on the other. The intermediate miles were marked with smaller stones having a P on one side and an M on the other. The stones were all sent from England. In November, 1782, Col. Alexander McClean of Pennsylvania and Joseph Neville of Virginia ran the remaining part of the line, which was tested and corrected by astronomical observations, and permanently marked, in 1784. In 1849 the former surveys were revised, and found correct in all important points.