The land grant given to Lord Baltimore stated that the Potomac River to its headwaters was to be the southern boundary of Maryland.

For many years, the North Branch was considered the main bed of the river, and Maryland's southern boundary was set there.

They carved the letters "Ffx" and Lord Fairfax's coronet into a large pyramidal rock and placed it at the center of these headwaters.

[11][15] Maryland and Virginia passed legislation in the early 1850s asking the federal government's help in establishing the true border in the area.

But he concluded that Maryland's legislative statements were unpersuasive in the face of a de facto boundary treated as such by landowners.

"True it is, that, after the running of the Deakins line, certain steps were taken, intended to provide a more effectual legal settlement and delimitation of the boundary.

"[30] Citing State of Rhode Island and Providence Plantations v. Commonwealth of Massachusetts again, Day noted that "a right in its nature prescriptive has arisen, practically undisturbed for many years, not to be overthrown without doing violence to principles of established right and justice equally binding upon states and individuals.

"[30] As for West Virginia's cross-claim that its boundary was the high-water mark on the far shore of the Potomac River, Day found Morris v. United States, 174 U.S. 196 (1899), conclusive and dismissed the claim.

[31] The majority held that a commission of surveyors should be appointed to permanently mark the Deakins line from the Fairfax Stone to the Pennsylvania border.

[32] The Supreme Court appointed a team of surveyors to survey the new boundary, and establish it by placing granite slabs every half-mile.

The U.S. Supreme Court held that Virginia had maintained its sovereignty over its riparian rights by continuously protesting Maryland's assertion of jurisdiction.

[34] The Supreme Court in Maryland v. West Virginia also applied a legal principle known as "prescription" to the boundary dispute.

[36] Although some legal scholars have attempted to provide criteria which would trigger prescription (e.g., 50 years of uninterrupted possession), in Maryland v. West Virginia the Supreme Court held that such decisions must be intensively fact-specific.

[37] Maryland v. West Virginia is also a classic case of the high court applying the legal rule of de minimis non curat lex.

The de minimis rule was commonly used by the U.S. Supreme Court in the 19th century in areas such as contract, admiralty, and property law.