MASDIX Arc Line Stone 5, 1765, DE-MD, is a roughly dressed stone set by Charles Mason and Jeremiah Dixon to demarcate the DE-MD boundary along the “Arc Line” segment of the boundary between Cecil County, MD and New Castle County, DE. The stone is located on the property of the Stine-Haskell Labs, a facility of Du Pont, and about 2.5 miles southwest of downtown Newark, DE. The stone is in both the NGS and Geocaching databases as station BOUNDARY ARC STONE 2 DE MD, PID = JU3849: (
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The stone is about 14 inches across at the bottom and eight inches thick, with a rounded top and no apparent inscriptions. It projects about 14 inches, and leans about five degrees to the south. The NGS and Delaware Geological Survey datasheets are silent with respect to the stone’s composition, but, to me, it appears to be of amphibolite gneiss. The stone sits in a split-rail fence enclosure in a wooded in the western portion of the laboratory’s property.
This stone has the oldest “Monumented” date in the NGS database: 01/01/1765, as does its companion, BOUNDARY ARC STONE 2 DE MD, PID = JU3851. Mason and Dixon surveyed this position on or about June 5, 1765, and set this stone on or about June 18, 1765.
To reach the Stine-Haskell Labs from Exit 109 off Interstate Highway 95 south of Newark, DE, go northeast on MD State Highway 279 for about 1.15 miles to the MD-DE boundary line. Continue northeast, now on DE State Highway 2, for about 0.8 miles to the Stine-Haskell main gate on the left. The Stine-Haskell Labs is a secure facility: travel beyond the main gate is possible only under escort from armed security personnel. They know where the stone is located.
HISTORY OF THE ARC LINE
The Arc Line forms a small portion of the boundary line between Delaware and Maryland. It is a 1.47-mile segment of the Twelve Mile Circle boundary line centered on the courthouse at New Castle, DE. It is centered at the western-most point of the Circle, and is marked with nine surviving historical stones (sharing two each with the Tangent Line and North Line) that are described below.
In 1750, after 70 years of dispute and failed negotiations between the proprietors of Delaware and Pennsylvania (the Penn Family) and the proprietors of Maryland (the Calvert Family), the Court of Chancery (equity) ruled on the boundary definitions for those three colonies. Among the Court’s determinations were (paraphrased):
a. The Twelve Mile Circle forming the northern boundary line of Delaware with Pennsylvania was to be centered on the cupola of the New Castle courthouse and measured horizontally as a radius,
b. The southwest corner of Delaware was to be the “Middle Point” of a line to be run from Cape Henlopen on the Atlantic coast (the modern Fenwick Island) across the Delmarva Peninsula,
c. The western boundary of Delaware was to be a line (the “Tangent Line”) run northerly from the Middle Point to a point tangent (the “Tangent Point”) with the Twelve Mile Circle,
d. The Tangent Line was to be run due north (the “North Line”) from the Tangent Point until it intersected a line of constant latitude (the “West Line”) fifteen miles south of the most southerly point in Philadelphia,
e. If any portion of the Twelve Mile Circle extended west beyond the North Line, the area within the Circle would remain Delaware territory (it did, and the portion of the colony’s boundary that the extending Circle formed would later be known as the “Arc Line”), and,
f. The West Line, constituting the northern boundary line of Maryland with Pennsylvania, was to be a parallel of constant latitude fifteen miles south of the most southern point in Philadelphia, and was to extend from the northern end of the North Line westward to a point equal to five degrees of longitude west of the Delaware River.
The Court appointed four local surveyors to run the Transpeninsular Line and, then, to run the Tangent Line northerly to the Twelve-Mile Circle boundary line. In 1750-1751, the surveyors, John Watson and William Parsons of Pennsylvania and John Emory and Thomas Jones of Maryland, ran and marked the Transpeninsular Line. In 1760, the Court ratified the Middle Point. Mr. Watson and the other three surveyors then ran a twelve-mile radius from the New Castle courthouse and established the “Tangent Point”, where a line run a few degrees west of north from the Middle Point would intersect the Twelve-Mile Circle boundary line. In 1761, the surveyors began to run the Tangent Line but, after about two years’ work, the task proved to be beyond their technical abilities. In August, 1763, the proprietors of the two colonies engaged Charles Mason and Jeremiah Dixon to complete this line, and to survey and mark all the boundary lines between Maryland and the Penns’ two colonies.
In 1764, Mason and Dixon accepted the colonial surveyors’ determinations of the Middle Point and the Tangent Point and ran the Tangent Line. In June, 1765, Mason and Dixon ran a line due north from the Tangent Point and established both the Arc Line and the North Line segments of the Delaware-Maryland boundary line. That month, they also marked the Arc Line with five unmarked dark gray gneiss stones. In November, 1766, they added a standard limestone intermediate mile stone. This last stone also served to mark the 83rd mile north of the southwest corner of Delaware.
Mason and Dixon were assisted by three colonial surveyors: Joel Bailey, Jonathan Cope and William Darby. They also engaged the services of a small army of axmen, teamsters and other laborers.
In 1849, Lt. Col. J. D. Graham, US Corps of Topographical Engineers (USCTE), re-surveyed the Arc Line and the North Line. The USCTE survey set new stones at the north and south ends of the Arc Line, and an additional stone on the line about 0.7 miles north of the Tangent Point.
According to my calculations, the Arc Line is 1.467 miles long with a chord of 1.466 miles. At its widest, the sliver of land between the Arc Line and an imaginary line run due north from the Tangent Point is 118.3 feet. The area gained by Delaware from the specification that created the Arc Line is 14.01 acres.
The Arc Line was marked with nine historical stones, all of which survive:
1. The “Tangent Stone”, a granite 1849 US Corps of Topographical Engineers (USCTE) survey stone with PID = JU3840 (BOUNDARY MON 82 TANGENT STONE).
2. Abutting the Tangent Stone is roughly-dressed gneiss stone set by Mason and Dixon in June, 1765. This stone does not have a PID.
3. About 0.4 miles north of the Tangent Stone, a stone with PID = JU4144, (BOUNDARY ARC STONE 1 DE MD RESET) originally set by Mason and Dixon in June, 1765. This stone lies in a chamber below the southwest-bound lanes of MD State Highway 279 / DE State Highway 2 (Elkton Road). The DGS describes the stone as an unmarked, obelisk-shaped piece of granite.
4. About 0.7 miles north of the Tangent Stone, a roughly-dressed gneiss stone with PID = JU3851 (BOUNDARY ARC STONE 2 DE MD) set by Mason and Dixon in June, 1765. It is a 7 x 12 x 20-inch, unmarked gneiss stone of the same type as the stone that abuts the Tangent Stone.
5. About 0.7 miles north of the Tangent Stone (and about 41 feet north of ARC STONE 2), a granite 1849 USCTE granite stone with PID = JU3852 (BOUNDARY ARC STONE 3 DE-MD).
6. About 1.0 miles north of the Tangent Stone, a dressed stone with PID = JU3850 (BOUNDARY ARC STONE 4, BOUNDARY MONUMENT 83). It is an intermediate mile marker set by Mason and Dixon in November, 1766. It is a 12-inch by 12-inch Portland Stone shaft that projects about 15 inches, and has a cut “M” on the west face and a cut “P” on the east face.
7. About 1.1 miles north of the Tangent Stone, an unmarked stone with PID = JU3849 (BOUNDARY ARC STONE 5 DE MD) set by Mason and Dixon in June, 1765.
8. About 1.4 miles north of the Tangent Stone, a stone with PID = JU3846 (MD SEL BDRY INTERSEC STONE 2). It is an 1849 USCTE stone, and is known locally as the “Prism Stone”. It is a three-sided granite shaft that projects about 24 inches. It has a cut “D” on the southeast face, a cut “M” on the west face, and a cut “P” on the north face.
9. At the Prism Stone, a roughly-dressed stone with no PID, but identified by the Delaware Geological Survey as the stone that Mason and Dixon set on this spot in June, 1765. It is an 8 x 12 x 44 dark gray gneiss stone, and is lying on its side in a wood cradle a few feet from the Prism Stone. It is of the same shape and material as Arc Stone 2.
According to the 1994 boundary agreement between Delaware and Maryland, the surviving Mason-Dixon and Graham Survey stones continue to mark this portion of the two states’ common boundary line.
References: Mason, Charles and Jeremiah Dixon, “The Journal of Charles Mason and Jeremiah Dixon” , transcribed by A. Hughlett Mason (American Philosophical Society, 1969); Danson, Edwin “Drawing the Line: How Mason and Dixon Surveyed the Most Famous Border in America” (John Wiley & Sons, 2001); Wikipedia articles “Mason-Dixon line” at (
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visit link) ; Mackenzie, John “A brief history of the Mason-Dixon survey line” (University of Delaware, 2002 (?)) at (
visit link) ; Scharf, J. Thomas, History of Delaware, 1609 – 1888, Chapter XI, “Boundary Disputes and Settlement”, (L.J. Richards, 1888) at (
visit link) ; Cummings, Hubertis M., “The Mason and Dixon Line – A Story for the Bicentennial”, (Commonwealth of Pennsylvania, 1962); and miscellaneous National Geodetic Survey datasheets and historical signs.
Also, the “State Boundaries” section of the Delaware Geological Survey (DGS) website at (
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