The first maps used symbols to characterize single outcrops; later maps introduced shaded areas to display the distribution of specific rock-types, but due the high printing-costs these maps were printed only in black & white, making them hard to read.

Maybe the first colored map was hand drawn by the German mineworker and later mine inspector Christian Lommer (1741-1786) in 1768, as a supplement to his travel account to the mining districts of Saxony. Lommer identified various mineral-localities and also distinguished between basic rock- types: granite - shown with an area colored in red, basalt - black, slate - blue, limestone -brown and sand with a dotted signature. Lommer was inspired in part by the appearance of the rocks, as basalt is often dark in color and also the signature for sand seems obvious, other colors seem to be used just for convenience.

However this map was never intended for a wider distribution or larger public and only one copy survives today.

In the following years other naturalist produced regional maps with "rock-colors" added to make them easier to read, especially to the aristocratic landowners (interested in the distribution of resources on their properties and potential buyers of the costly maps). The Freiberg Mining Academy was one of the first scientific institutions were this method was widely adopted. In 1775 a former student of the Academy became professor there - the famous Abraham Gottlob Werner (1749-1817). Werner not only established a basic rock classification scheme but also proposed a specific color scheme to display these rock-types. With Werner the Freiberg Mining Academy became the most important geological institution of the time and not only German, also many foreign naturalists visited the academy and attended lectures there. Soon the color scheme as proposed by Werner was known by most geologists of the time.

Fig.1. Key for the lithological map of Saxony (1778), by naturalist Johann Friedrich Wilhelm von Charpentier (1738-1805, a colleague of Werner at Freiberg), where he adopted a color scheme similar to the one as proposed by Werner over the years.

In 1820 the lawyer and amateur geologist Christian Keferstein (1784-1866) contacted the mining inspector Johann Wolfgang Goethe (1749-1832, today better known for his literary work) for help in the publication of an ambitious work - a geological atlas with a set of maps of Central Europe. Goethe was also working on color theory and Keferstein was interested in the opinion of the celebrated artist which colors to use in his maps. Goethe, influenced by the teachings of Werner, worked almost one year on the problem and in July 1821 the first edition of the atlas, entitled "Teutschland geognostisch geologisch dargestellt, mit Charten und Durchschnittszeichnungen, welche einen geognostischen Atlas bilden" (Atlas of Germany in a geological representation, with charts and sections) was published.

Keferstein writes in a later letter to Goethe:

"What I just imagined, but impossible for me to realize - the harmony of colors - with your help it was accomplished…[]… Your color table will remain a classic work, when my contributions will be already forgotten…"

This publication - and the therein used color scheme of Goethe and Werner - will influence geological mapping for decades to come. Even today some colors first adopted by the early 19th century geologists and publicized by the geological atlas of 1821, like red for igneous rocks or blue for limestone, are still in use.

Fig.2. Key for the lithological map of Central Europe by Keferstein (1821).

Comparison of different color schemes in time, as proposed by Werner in various publications, as used by Johann F.W. von Charpentier, as used by Spanish naturalist Carlos de Gimbernat (1768-1834, who had visited Werner and later draw one of the first geological maps of the Alps) and finally as published by Keferstein, based on a scheme modified by Goethe.

Rock-type Colors by WERNER Colors by CHARPENTIER (1778) Colors by GIMBERNAT (1808) Colors by KEFERSTEIN (1820/21) Schist greyish green orange green green Granite red red reddish-pink red Porphyry brown - orange grey Sandstone yellow yellow yellow orange Limestone blue blue blue blue Basalt black - grey black

Bibliography:

BAUMGARTEN, B. (2007): Carlos de Gimbernat and the first geological map of Tyrol (1808). Geo.Alps, Sonderband 1: 1-10

OLDROYD, D. (2013): maps as pictures or diagrams: The early development of geological maps. In BAKER, V.R. ed, Rethinking the fabric of geology: Geological Society of America Special Paper 502: 41-101

STEINER, W. (1997): Die erste geologische Karte Mitteleuropas wurde im Jahre 1821 im Bertuch´schen Verlag des Geographischen Instituts in Weimar gedruckt. Stadtmuseum Weimar : 1-4