In coming over by railroad from the Chesapeake to the Delaware, the train, after crossing the broad Susquehanna and the head of Elk, and rounding in Maryland the Northeast Arm of Chesapeake Bay, soon enters the State of Delaware near the northeastern corner of the former State. This corner is at the termination of the crescent-shaped northern boundary of Delaware. The northern boundary of Maryland here beginning and laid down due west, to separate it from Pennsylvania, is the famous "Mason and Dixon's Line," surveyed by Charles Mason and Jeremiah Dixon, two noted English mathematicians and astronomers in the eighteenth century. This boundary gained great notoriety because it so long marked the northern limit of slavery in the United States. For almost a century there were conflicts about their respective limits between the rival proprietaries of the two States, producing sometimes riot and bloodshed, until, in 1763, these men were brought over from England, and in December began laying out the line on the parallel of latitude 39° 43' 26.3" North. They were at the work several years, surveying the line two hundred and forty-four miles west from the Delaware River, and within thirty-six miles of the entire distance to be run, when the French and Indian troubles began, and they were attacked and driven off, returning to Philadelphia in December, 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 by smaller stones, having a P on one side and an M on the other, all the stones thus used for monuments being sent out from England. After the Revolution, in 1782, the remainder of the line was laid down, and in 1849 the original surveys were revised and found substantially correct.