This map, titled Geologische Karte der Vereinigten Staaten und Britischen Provinzen von Nord-Amerika, is based upon a map created by Jules Marcou in July 1855, and here republished by Justus Perthes in Gotha for Petermann. It represents a geological survey of the United States and British provinces of North America, illustrating the varied geological formations across the continent. The map is color-coded to depict different geological eras and formations, using a key to differentiate between the various rock types and their respective geological periods.
Jules Marcou (1824–1898) was a prominent Swiss-American geologist known for his pioneering geological studies in North America. Marcou's work was significant during a time when geological mapping was still in its formative stages. He was one of the first geologists to traverse large parts of the United States and Canada, meticulously documenting the geological characteristics of the land. Marcou's maps were among the earliest attempts to provide a comprehensive geological overview of North America, contributing substantially to the understanding of the continent's geology during the mid-19th century.
Marcou's career was marked by both notable achievements and controversy. He conducted extensive fieldwork in North America, supported by institutions such as the Smithsonian and the Boston Society of Natural History. His contributions include multiple geological maps and publications, but some of his interpretations and classifications were criticized by his contemporaries for inaccuracies. Despite this, Marcou’s work laid important groundwork for future geological exploration and mapping in North America.
Explanation of Color Coding
The map employs a detailed color-coded system to represent various geological formations, which is explained in the key labeled "Farben-Erklärung" (Color Explanation). The colors and their corresponding formations are as follows:
-
Neue Gebilde (Modern Terrain): This is marked in a green shade, representing the most recent geological formations.
-
Tertiäre Gebilde (Tertiary Terrain): Colored in yellow, this denotes Tertiary period formations, which are typically from around 66 to 2.6 million years ago.
-
Kreide-Formation (Cretaceous Terrain): Represented in a light green, these formations are from the Cretaceous period, dating from about 145 to 66 million years ago.
-
Jura-Formation (Jurassic Terrain): Shaded in blue, this color indicates Jurassic formations from approximately 201 to 145 million years ago.
-
Neuer rother Sandstein (New Red Sandstone): This is indicated in bright yellow, highlighting formations characterized by red sandstone, often associated with the Triassic period.
-
Steinkohlen-Gebirge (Coal Measures): Represented in dark brown, this color identifies coal-bearing formations, often from the Carboniferous period, significant for their economic value as sources of coal.
-
Kohlen-Kalkstein (Coal Limestone): Shown in a hatched gray pattern, representing limestone formations associated with coal beds.
-
Devonische Schichten (Devonian Terrain): Shaded in red stripes, these formations date back to the Devonian period, roughly 419 to 359 million years ago.
-
Silurische Schichten (Silurian Terrain): Represented in blue stripes, indicating rocks from the Silurian period, dating from about 443 to 419 million years ago.
-
Vulkane (Volcanic): These formations are marked in bright red, showing areas with volcanic rock.
-
Kupfer-Trapp (Copper Traps): Indicated in deep red, representing copper-bearing trap rocks, which are igneous formations.
-
Granit u. metamorph. Gestein (Granite and Metamorphic Rocks): Marked in light pink, these colors denote areas with significant granite and metamorphic rock formations, typically associated with ancient geological activity.
This map not only serves as a geological reference but also provides insight into the distribution of key mineral resources and the geological history of North America as understood in the mid-19th century. The comprehensive use of color coding allows for a clear visual differentiation of the diverse geological landscapes across the continent, reflecting Marcou’s detailed and ambitious attempt to chart the region’s complex geology.