The Oregon Surveyor | Vol. 38, No. 1, 2015 18 THE EPIC SURVEY OF MASON AND DIXON Aft er setting the Post Mark’d West, Mason and Dixon then headed south to the middle point of the peninsula that had been previously marked by the colonial surveyors. Following a convenient star, they ran a dead straight line 83 miles from the midpoint, a feat that had never been accomplished before. By measuring their error at the end and proportioning it back along the length of the line, they were able to set the tangent line. Th ey measured the angle at the tangent with their Hadley Quadrant, and the angle measured a perfect 90 degrees. Mason and Dixon had successfully found the solution that had eluded the colonial surveyors. In March 1765, a year and a half aft er their arrival, they returned to the Post Mark’d West to begin the monumental task of running the west line. Off they went, hacking their way through the primal forests of western Maryland. Th ey travelled in wagons, the delicate instruments atop a feather mattress. As they went, Mason and Dixon set boundary stones. Mile stones were marked “M” on the Maryland side and “P” on the Pennsylvania side, and they set “crown stones” every fi ve miles with the coat of arms of the Calverts on one side and the seal of the Penns on the other. Aft er nine months of work on the west line, they had proceeded 117 miles, 12 chains, and 97 links from the Post Mark’d West. (Like other surveyors of their day, Mason and Dixon measured with a chain that had been standardized at 66 feet and was divided into 100 links.) Th ey stored their instruments, returned back east to the Harland Farm where they spent the winter, and then resumed in the spring. On June 18, 1766, Mason and Dixon reached the Allegheny Mountains, which was the frontier—the western limit of English sovereignty and the beginning of Native American control. Negotiations with the Indians proceeded slowly, but fi nally, greased by a payment of 500 pounds sterling, a treaty was signed and permission secured to proceed beyond the Alleghenies. In July 1767, the Indians dispatched three Onondagas, eleven Mohawks, and an interpreter to guide the survey party, which had now grown to 115 men. Early in October, the party crossed Dunkard Creek, where they encountered the Great Warrior Trail. Th is was one of the most important Indian trails in the country, running from New York to South Carolina. Th e Indians’ chief informed the surveyors that the trail “was the extent of his commission from the Chiefs of the Six Nations and that he would not proceed one step further westward.” Mason and Dixon continued on and extended their line an additional 250 feet to the top of the next ridge, Brown’s Hill. Aft er the surveyors set up a tall post and a conical mound at 233 miles, 17 chains, and 48 links from the Post Mark’d West, the Mason-Dixon line came to an end. Having fi nished their work, Mason and Dixon returned to Philadelphia, where they drew a map of their survey. Two hundred copies were printed. Th e magnitude of Mason and Dixon’s accomplishment is almost impossible to imagine. Th ey spent nearly fi ve years in America, living in tents and enduring searing summers and frigid winters. Today, we use GPS to calculate a latitude in minutes. It took Mason and Dixon two weeks of celestial observation and complex hand calculations to accomplish the same task. Long before chain saws were invented, they used hand axes to clear a vista 16 feet or so wide and more than 330 miles long. Th eir line has been resurveyed many times, and the accuracy that they achieved, given the technology of their day, continues to astound. Mason departed for home on September 11, 1768, the work complete. He wrote in his journal “at 11h 30m a.m. went on Board the Halifax Packet Boat for Falmouth. Th us ends my restless progress in America.” Dixon returned to his family and surveying practice in County Durham, where he died in 1779. Mason returned to America in 1786 with his wife and eight children. He died shortly thereaft er and is buried in an unmarked grave in the Christ Church burial ground in Philadelphia. However, the surveyors’ line lived on. In 1820, Congress adopted the Missouri Compromise and fi rst used the term “Mason-Dixon line” to describe the Maryland-Pennsylvania border. States north of the Mason- Dixon line were to be free, and those south slave states. And so in addition to being the fi rst geodetic survey in the New World and one of the greatest scientifi c and engineering achievements of all time, the Mason-Dixon line became an icon—the dividing line between slavery and freedom. ◉ David S. aler, P.E., F.NSPE, is president of D.S. aler and Associates Inc., a civil and environmental engineering rm in Baltimore. A Fellow of the American Society of Civil Engineers and a licensed surveyor, he is also a guest scholar at the University of Baltimore School of Law, where he lectures on land use. » THE EPIC SURVEY OF MASON AND DIXON, from page 17 Journal of Charles Mason and Jeremiah Dixon, 11/15/1763 to 09/11/1768
PLSO Issue 1 2015 Jan_Feb
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