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Measuring the Index Line at Logansport

Map Logans Ferry
The Observatory at Logan's Ferry measured the Index Line from a Congressional Map Book in 1843 (LOC).

From its early beginnings in 1830, Logansport was known as Logan's Ferry. Sitting along the Sabine River, it was a major crossing point for folks going to and from Texas before and after Texas became a Republic. But, due to the 1811 Louisiana Constitution, the 1819 Adams Onis Treaty, the Mexican Revolution of 1821-1828 AND the Texas Revolution of 1836, the exact place of where western Louisiana gave way to eastern Texas had not been precisely measured.


Apparently, surveyors aren't keen on simply writing "the Sabine River" when explaining boundaries. And, the Sabine River flows all the way to today's Hunt County, so therefore it couldn't be used as a boundary beyond its north/south flow. There have to be latitudes and longitudes, gosh darnit! The lack of a verified boundary also confused land claimants in Texas, which still used the Spanish survey system, and Louisiana, which by and large had adopted the American system.


In 1840, Major J.D. Graham and Lt. Col. Kearney were tasked by the U.S. Congress through the Louisiana Geodetic Survey Commission to take their measurements in line with the earth's sphere, using Airy and Everest as reference points. They were thus able to line up their coordinates with measurements taken in 1830. This, then, officially established the boundary line between Texas and Louisiana along a cardinal line above the Sabine River. Called the Index Line, it stretched all the way from Logansport north to the Red River.


As I was looking at a map of the area north of Logan's Ferry that the U.S. Congress published in 1840 I noticed that there was a "Camp Graham" beyond the swamp and aligned with the Index Line. This is, I believe, where Major Graham and his group of surveyors set up his instruments. Notice the "observatory" that was marked near the camp.


After the survey was over, the camp did not remain active, but it still counted as an important site to surveyors and mappers. During the Civil War, the site briefly became "Camp Worth."


There is no such thing as a simple map. They all tell stories! Link to the map in its entirety: https://www.loc.gov/resource/g3700m.gct00284/?sp=142&r=-0.03,0.093,1.246,0.576,0

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