Mason & Dixon: Their Line And Its Legend


From the end of our line to the Ohio on a West Course is about forty miles … This West Line … if extended would … pass through the Southern part of the Illinois. The distance about 7 or 800 miles. A country says my informer thro’ which you may travel 100 Miles, and not find one Hill, or one Acre of barren land.

The survey itself was not destined to go much farther. Shawnee war parties were reported to be active, and the escorting Senecas and Delawares had no intention of running into them. A sizable group of Indians had made up the escort, but throughout August and September there was a steady flow of departures. Mason and Dixon prevailed upon their axemen to stay with them, however, until on October 9, 1767, they reached the mouth of Dunkard Creek about thirty miles east of what is now Pennsylvania’s southwest corner. Here the remaining Indians unanimously declared that the line could not be extended farther. The Englishmen accordingly took their final observations—“233 Miles, 3 Chains and 38 Links from the Post mark’d West.”

Winter came early in the high altitudes, and as Mason and Dixon worked their way back eastward, foot-deep snow hampered them. It was not possible to convey the remaining limestone markers to the western-most part of the line, so mounds of earth and rocks were constructed to identify the border. By the end of December they were able to report to the joint commission that the work had been completed. The final request of the commission was that Mason and Dixon prepare a map of the border for an engraver and that they provide the commission with the length of a degree of longitude along the “West Line.” The map was completed within a few weeks. As for the longitude measurement, Mason and Dixon reported with proper scientific qualification:

By comparing our measuration of a Degree of the Meridian with that made under the Arctic Circle, supposing the Earth to be a Spheroid of an uniform Density: a Degree of Longitude in the Parallel of the West Line is 53.5549 Miles. But as the Earth is not known to be exactly a Spheroid, nor whether it is everywhere of equal Density, and our own Experiment being not yet finish’d; we do not give in this as accurate. [The modern value is 53.2773 statute miles.]

It was accurate enough to satisfy the commissioners, who indeed pronounced themselves highly gratified with the entire project. From England the Penns took pains to send Mason and Dixon a letter of appreciation. Mason himself was elected to membership in the American Philosophical Society—quite possibly through the suggestion of Benjamin Franklin.

Although the survey ended the Pennsylvania-Maryland-Delaware border dispute, the original charter prepared for George Calvert, first Lord Baltimore, continued to play tricks. This document had put the western limits for Maryland at “the first fountains of the Pattowmack,” but the Potomac River has so many forks and branches that unanimity of opinion could hardly be expected as to just what point was represented by this specification. The Mason-Dixon survey actually ran about thirty miles west of what was finally fixed by the United States Supreme Court, in 1912, as the northwest corner of Maryland. And so, as it turned out, the Calverts had paid half of the cost of a portion of the survey which had no bearing on their territory. For both proprietors it was an expensive undertaking, costing in all the equivalent of at least $100,000 in modern currency.

On September 11, 1768, four years and ten months after their arrival, the English geodesists sailed from New York for Falmouth. In London, on November 11, they submitted a final bill for £3,512/9 s., including passage money. Both proprietors willingly paid. In August, they already had joined in a petition to the King in Council to ratify the settlement of the border along the line surveyed. The royal ratification had no legal effect, but both sides seemed to feel that a seal of approval had been placed on the whole.

The daily progress of the survey had been recorded in a set of field notes kept by Mason, from which a final report was made to the commissioners. This journal was almost lost to posterity. Following the preparation of the “fair copies” of the field data for deposit with the two proprietaries, Mason or his descendants either lost or discarded the original manuscript. In 1860 it turned up in Halifax, Nova Scotia, among a pile of papers consigned to a trash heap. It was included among the Canadian exhibits at the Philadelphia Centennial in 1876, where it was called to the attention of Hamilton Fish, Secretary of State. After a brief negotiation with its owner, Judge Alexander James of the Supreme Court of Nova Scotia, the State Department purchased it for five hundred dollars in gold. It is now on file in the National Archives.