The Oregon Surveyor | Vol. 38, No. 1, 2015 16 THE EPIC SURVEY OF MASON AND DIXON navigability of the Delaware River, lay about fi ve miles south of the actual 40th parallel. Depending on the location of its border, Pennsylvania could have lost both Philadelphia and its critical access to the sea and ability to resupply. Finally pressed by the king’s council, in 1732 the parties entered into an agreement. Th ey decided that the boundary should run 15 miles south of Philadelphia (the east-west line), west from Cape Henlopen on Fenwick Island to the midpoint of the Delmarva peninsula (the transpeninsular line), and then north to intersect a tangent with the 12-mile arc around New Castle (the tangent line). Th is was not a good deal for the Calverts, as it placed the boundary about 19 miles south of the true 40th parallel. Th e controversy raged on. Th e parties could not come to a resolution, and fi nally in 1735 the Penns fi led a complaint in the English courts that became known as the Great Chancery suit. Th e case was litigated over 15 years at enormous expense, until in 1750 a decision was rendered. Th e southern boundary of the lower three counties of Pennsylvania (now Delaware) would be at the latitude of Cape Henlopen, and the peninsula would be divided equally. Th e center of the 12-mile circle would be measured as a radius from the center of New Castle (which was agreed to be the dome of the courthouse), and the east-west line would run at a constant parallel of latitude, 15 miles south of the southernmost point of Philadelphia. Th e proprietors engaged local surveyors who started with the transpeninsular line in April 1751. Th ey began on Fenwick Island and ran their line across the peninsula from the “verge” of the Atlantic Ocean to the Chesapeake Bay. Although swamps and dense vegetation made work on the line diffi cult, the colonial surveyors were able to fi nd and mark the midpoint of the peninsula, which became the southwestern corner of what is now Delaware. Th e colonial surveyors next tackled the task of running the tangent line, which ran from the midpoint of the peninsula to the point of tangency with the 12-mile circle around New Castle. Th is was a lot harder than it looked on paper given that the line was more than 80 miles long, the terrain diffi cult, and the equipment poor. Th e geometry of the corner was also very complex. An 83-mile-long line would have to be run to just graze the 12-mile circle at a perfect 90 degrees. Th is would then have to be run north to intersect another line exactly 15 miles south of Philadelphia. Th e colonial surveyors ran their line from the midpoint of the peninsula due north until it was within the 12-mile radius. Th en they measured from the dome of the courthouse, but their fi rst attempt was a half mile too far east. » THE EPIC SURVEY OF MASON AND DIXON, from page 15
PLSO Issue 1 2015 Jan_Feb
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