[1] Pennsylvania's Charter (1681) specified that the colony was bounded "on the South by a Circle drawne at twelve miles [19 km] distance from New Castle Northward and Westward unto the beginning of the fortieth degree of Northern Latitude, and then by a streight Line Westward...."[2] Later surveys established that the town of New Castle in fact lay a full 25 miles (40 km) south of the fortieth parallel, setting the stage for a boundary dispute.

[3] Because the fortieth parallel lay north of the city of Philadelphia, Maryland pressed its claim most seriously in the sparsely inhabited lands west of the Susquehanna River.

By the late 1710s, rumors had begun to reach the Pennsylvania Assembly that Maryland was planning to establish settlements in the disputed area near the river.

In response, Pennsylvania attempted to bolster its claim to the territory by organizing a proprietorial manor along the Codorus Creek, just west of the river, in 1722.

They had been coming to the birding swarms along the Conejohela Flats since 1724 and had made friends and converted an appreciable number of Indians, most by working their way through the marshy shallows on the opposite (west or right) bank of the Susquehanna.

[citation needed] Settlement picked up significantly that year, probably due to the promise of regular ferry service across the Susquehanna, greatly easing transportation difficulties, but the inflow alarmed Lord Baltimore with respect to his ability to assert control and collect incomes from the disputed area.

Sixty yards into the trip, the Pennsylvanians turned their guns on the Marylanders and a fight ensued with Cresap attempting to use the oars to defend himself.

Although the magistrate eventually signed warrants that brought the two Pennsylvanians to court, he first stated that "he knew no reason he (Cresap) had to expect any justice there, since he was a liver in Maryland.

Significantly, Cresap filed charges with Maryland authorities, claiming that Pennsylvania officials had conspired with the attackers and with local native tribes to drive him from the area.

"[11] Depositions of several Germans accuse Cresap and his relatives, the Lowes, of maltreatment:[8] Two incursions of Maryland militia into present day York County, Pennsylvania are mentioned in depositions by Pennsylvania natives:[8] Cresap first obtained a patent from Maryland for a ferry at Peach Bottom, near the Patterson farm, then shot several of Patterson's horses.

[12] Cresap continued his raids, destroying barns and livestock, until Sheriff Samuel Smith raised a posse of 24 armed "non-Quakers" to arrest him on November 25, 1736.

"[12][13] Following Cresap's arrest, Maryland sent a petition to King George II requesting that he intervene to restore order pending the outcome of the Chancery suit.

In response, the royal Committee for Plantation Affairs organized direct negotiations between the two colonies, which resulted in the signing of a peace agreement in London on May 25, 1738.

[15] Because Blue Rock Ferry lay well to the north of the provisional boundary, Cresap did not return to the area following his release in the prisoner exchange.

In 1750, the Chancery Court upheld the validity of the 1732 agreement, which became the basis on which Charles Mason and Jeremiah Dixon surveyed the permanent boundary (the Mason–Dixon line) between Pennsylvania and Maryland in 1767.