Digital Edition Exclusive: 31 Degrees of Latitude

October 8, 2009
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The western portion of the southern boundary from Ellicott’s journal, 1814, second edition.


At the conclusion of the American Revolutionary War, the newly formed United States government struggled to define the nation’s boundaries--particularly in the south where other governments claimed land on the North American continent.

The Treaty of San Lorenzo signed in 1795 between the United States and Spain contained two provisions that were important to these efforts.

First, United States citizens had the right to use the Mississippi River to access the ocean through what was then Spanish territory for commerce and transportation. This access was necessary to prevent secessionists in the western regions of the United States from breaking away from the newly created Union to align with Spain for that right.

Milton Denny at a mound location.

Second, an agreed boundary was established between the two nations. This boundary began at the Mississippi River on the 31st latitude and followed that parallel east to the Chattahoochee River, the current border between Alabama and Florida. The boundary continued south along the center of the Chattahoochee River until its junction with the Flint River. From there, the boundary headed east to the headwaters of the St. Mary’s River (the current boundary between Georgia and Florida) and then followed the middle of the St. Mary’s River until it emptied into the Atlantic Ocean.

The treaty was ratified on April 25, 1796. Article III of the treaty set up a joint boundary commission with a commissioner and surveyor provided by both nations that was to meet in Natchez (in what would soon be the Mississippi Territory) before six months had elapsed from the ratification date. This set a meeting date of no later than Oct. 25, 1796 at Natchez.

The U.S. Secretary of State, Timothy Pickering, appointed Andrew Ellicott, the leading U.S. expert in running parallels of latitudes, as commissioner and gave him written instructions dated Sept. 14, 1796. These instructions said Ellicott was to, if possible, “run and mark one continued boundary line from the Mississippi to the St. Mary’s.” If this task was not possible, Ellicott was instructed to at least mark where the boundary crossed at the “great rivers” between the Mississippi and Chattahoochee. And, for the land boundary between the Flint and the St. Mary’s, he was to mark it throughout its course recognizing it didn’t follow a particular latitude. The monuments were to be stone if attainable and, at other points, earthen mounds.

Ellicott left home on Sept. 16--two days after the date of the instructions--to make his way to Natchez. He finally arrived in Natchez on Feb. 24, 1797, but he didn’t start running and marking the line until April 9, 1798--more than a year later. The Spanish were delaying their implementation of the treaty, expecting secessionist plans undertaken by their spies to succeed. Ellicott’s steadfast resolve in carrying out his instructions to survey the boundary in the face of Spanish intimidation was instrumental in the failure of the spies’ plans.

The Ellicott Stone. Photos by Larry Crowley.

Ellicott's Field Survey

When the survey began in April 1798, what lay ahead was 381 miles of boundary to the Chattahoochee River, then another 155 miles from the Flint to the St. Mary’s River--a total land boundary of 536 miles. The method selected by Ellicott was a careful laying out of the latitude to be monumented at 1-mile intervals by offsets from a chord line to the arc of latitude intersecting at 10-mile intervals. The 10-mile intervals allowed the offsets to be marked within a cleared 60-foot-wide swath of land after the timber had been burned.

This method proved extremely slow. Each mile of survey required more than seven acres of land to be cleared; it took 158 days to complete the first 20 miles. At that rate, the complete survey would take 12 years and require clearing close to 4,000 acres of land. It was too much for the Spanish surveyor, a local property owner named William Dunbar. He quit on Sept. 1, 1798 and went home.

At the end of the 21st mile, Ellicott resorted to a less scientific method. This method traced a line east using a survey compass to establish a guide line. At the major rivers, an astronomic observation would be made to determine the true location of the 31st parallel and an offset correction calculated from the guide line. A party, headed by his associate named Gillespie, would proportion that correction back down the guide line to pull offsets at each mile and erect earthen mounds on the boundary.

The eastern portion of the southern boundary from Ellicott’s journal, 1814, second edition.

The first guide line oriented by a surveyor’s compass traversed 85 miles to the east side of the Pearl River where Ellicott used his small zenith sector to determine that the guide line was only 203.2 feet north of the 31st parallel. (The large zenith sector had not yet shown up at the location. It was too heavy to carry overland, so it was transported by water.) This correction amounted to a northern drift of 2.3 feet per mile--equivalent to a little over 1.5 inches out of alignment every 100 yards, which, in today’s terms, is the distance between the goal lines of a football field. The data confirmed to Andrew Ellicott that sufficient accuracy could be achieved using this method. It took only 57 days to survey this 85 mile stretch of the line, which equated to 1.5 miles per day.

On Dec. 15, 1798, the last observations were made at the Pearl River. Ellicott sent Gillespie with a group of laborers back down the guide line to pull the offsets and erect the mounds. The task of carrying the line forward toward the east was given to Daniel Burnet. Ellicott went down the Pearl River to New Orleans to arrange for provisions, acquire an ocean-going vessel and jointly sign a report with the Spanish commissioner detailing the work completed so far. He would not make it back to the line until March 18, 1799, when the work was 100 miles further east at the Mobile River.

Larry Crowley at a mound location. Photo by Milton Denny.

Observations at the Mobile River revealed that Burnet was not as proficient in running the compass line alone as when under the direction of Ellicott. The line was observed to be 8,556.1 feet north of the 31st parallel. Using the same 100-yard football scale to illustrate relative accuracy, the departure would be 4.9 feet out of alignment in that distance. This offset of 8,556.1 feet was pulled south and a permanent stone marker, now known as the Ellicott Stone, was erected at mile 206 on the east side of the Mobile River. This stone is still in place.

The next compass line was run 51 miles east to the Conecuh River (mile 257) after using triangulation to traverse the first 10 miles across the Mobile Delta. Ellicott left the field by traveling down the Mobile and next arrived with the field crew when observations were taken at the Conecuh River beginning on May 9, 1799. This compass line had better results, with a cumulative northern drift of only 236 feet over the 51 mile stretch of the boundary, although corrections were distributed over only the last 41 miles. This drift would compare to approximately 4 inches in a football-field length.

The last compass line segment ran on the 31st parallel boundary traversed 124 miles from the Conecuh to the Chattahoochee River. Ellicott arrived on the line on July 25, 1799, by traveling up the Chattahoochee. His observations there were completed on August 20, 1799, and indicated the guide line was 7,110.5 feet north of 31 degrees latitude. This drift north placed on a 100-yard football field is equivalent to 3.3 feet in that distance. Gillespie was sent back down the line to proportion the offsets from the guide line and erect the mounds.

Ellicott went down the Chattahoochee to establish the location of its junction with the Flint River. After completing the observations to establish the location on Sept. 16, 1799, the crew’s effort to run a land boundary from there to the headwaters of the St. Mary’s was abandoned. Ellicott sailed down the Chattahoochee and around the coast of Florida to meet a crew that went overland in the town of St. Mary’s on Dec. 9, 1799. The group traveled up the St. Mary’s River to establish its headwaters as the last work done on the boundary.

A concrete monument at a mound. Photo by Larry Crowley.

Finding the Mounds

It is a well-known principle in surveying that if the points established during the original survey are found, they will hold their position over all other evidence. Since the original survey and placement of the mounds in the Ellicott Line, a great deal of confusion has existed about their location. Many different attempts have been made to locate and document the mounds. In some cases, a cedar stake is called for in the center. None of these stakes has ever been found. In one case, the original GLO surveyors laying out Florida mistook the guide line run by the Ellicott crew for the mound line. This error resulted in the original Florida GLO surveyors laying out sections into Alabama by as much as 7,110.5 feet.

Originally piles of earth 4 to 5 feet high, most of the mounds are now only 4 to 6 inches high, so knowing their most likely positions is paramount to finding them. Recently, maps and plats have surfaced providing important information that has aided the location effort. The last three years have been spent developing a system utilizing these old maps and plats coupled with modern GPS technology, such as Topcon GR-3 receivers, as well as perches, chains, feet and meters, to find the most likely locations of the mounds.

At this time, eight of the original 120 earthen mounds have been found and their locations documented with GPS. Additional work is under way to locate the remaining mounds. Definitively locating the boundary will provide valuable information for the states of Alabama and Florida.


View this article in the digital edition here, www.nxtbook.com/nxtbooks/bnp/pob_200910/#/38.

Sidebar: Join the Search!

On Dec. 3-4, 2009, Auburn University’s Technology Transfer program will hold a seminar in Andalusia, Ala., to provide surveyors with the best information available to find the mounds. Attendees will be given a classroom overview of the mound line, provided with locations of some of the mounds and assigned to teams to find them. Attendees are asked to bring their own GPS equipment if possible. This event will provide an opportunity to work on a survey of great historical importance while walking in the footsteps of one of America’s great men of science.

For an electronic copy of the brochure detailing this event, visit eng.auburn.edu/distance-learning/ce/online-orders.html.

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