Geological Exploration of the Fortieth Parallel
The Geological Exploration of the Fortieth Parallel was a geological survey made by order of the Secretary of War according to acts of Congress of March 2, 1867, and March 3, 1869, under the direction of Brig. and Bvt.
Source: Wikipedia — Geological Exploration of the Fortieth Parallel (CC BY-SA 4.0)