This large and very colorful thematic map is the third edition of a map first issued in 1872 that, according to Marcou & Marcou. The map identifies forts, watershed, major towns and more. The legend at lower left provides an explanatory key to the colors used to indicate nine distinct geological formations, e.g. Eozoic, Cambrian, Devonian, Triassic, Cretaceous, Tertiary, Volcanics, etc. The carefully drawn map shows good geographical detail as well as remarkable geological information conveyed in strongly applied color. The geography of the map is from the War Department's "Military Map of the United States," used by permission of the Chief of Engineers.

References: Marcou & Marcou #70; Phillips (A) 1330

Condition: B+

The colored areas of the map are mint and flawless. The strong color has resulted in slight offsetting in blank oceans below the map.