This stunning geological map of Europe was produced in 1875 by Andre Dumont, a Belgian scientist and mapmaker. Dumont, who previously published a geological map of Belgium that took him 20 years to complete, was one of the first cartographers to successfully deploy the techniques of chromolithographic printing to represent geology in vibrant color. The map, which folds up into a case, is composed of 24 sections.
Writing on the topic of geological maps in the Bulletin of the United States Geological Survey in 1885, geologist Jules Marcou (also, incidentally, the original owner of the copy of the map that was scanned to create the digital image below) described the difficulties mapmakers faced in using color printing techniques effectively. Marcou called Dumont's map of Belgium "a real masterpiece of coloring" and this map of Europe "another fine example ... far superior to the one made at the same time in Edinburgh," the "Geological Map of Europe" by Sir Roderick Murchison and James Nicol. (That inferior map can be viewed here.)
Geologist David Bressan writes that the color scheme used in many geological maps derives from the work of Johann Wolfgang von Goethe, the writer who was also a mining inspector and color theorist. Goethe helped design the color scheme for a geological atlas of Germany that was published in 1821. Bressan argues that some aspects of Goethe's color-coding—"red for igneous rocks, blue for limestone"—took hold as common conventions used by future mapmakers. Indeed, Dumont's reds are igneous, and he assigned blue to the landscapes shaped during the Devonian period, which (like the Basque Mountains of the Iberian Peninsula) often feature limestone.
Click on the image below to reach a zoomable version, or visit the map's page on the David Rumsey Map Collection website.