Fourth Principal Meridian

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The Fourth Principal Meridian begins at a point on the right bank of the Illinois River, in latitude 40° 00' 30" north, and longitude 90° 28' 45" west from Greenwich, and with the base line running west from the initial point, governs the surveys in Illinois west of the Illinois River and west of that part of the third principal meridian which lies north of the river.

[edit] Source

• Raymond, William Galt (1914). Plane Surveying for Use in the Classroom and Field (via Google Books), New York: American Book Company.