The dominant role of Neptunism, denominated after the Roman god of the sea, in geology during the 18th and 19th century is ascribable to the significance of the Mining Academy in Freiberg (Saxony) and especially the teaching of one person: mine inspector and professor of mineralogy Abraham Gottlob Werner (1749-1817).
Fig.1. Frontispiece of "The Granite Controversy" by H. H. Read (1957), drawn by D. A. Walton. This cartoon is fitting to the 19th century controversy between Neptunism and Plutonism, however it was drawn to deal with the problem arose in the 20th century if granites are mainly of metamorphic origin.
His research and his lectures founded a classification-scheme of rocks based on their sequence of layers and their age, rather than by the types of minerals as had been previous practice. Werner was not the first to propose water as origin of the rocks, but he was the most consequent supporter and divulgator of this theory.
In his book of 1787 "Kurze Klassifikation und Beschreibung der verschiedenen Gesteinsarten." (Short classification and description of the various rock-formations) he proposes a classifications scheme for minerals and rocks, speculating on their formation and the formation of earth.
Werner explained the observable sequence of rocks by the theory of a primordial ocean. Early earth, born by the agglutination of cosmic matter, originally consisted of a primordial ocean with various dissolved matter, surrounding a solid nucleus. According to the Neptunism, all observable rocks were then deposited by crystallisation and sedimentation from this former universal sea in a specific order: first the oldest and hardest rocks - granites, gneiss and schist, then basalts and finally limestone and other common sedimentary rocks. After the last rocks crystallized out, the sea level dropped, and erosion begun forming the last, and more recent sedimentary rocks.
Johann Wolfgang Goethe, philosopher, poet and Neptunism geologist, summarizes the main argument as follows:
"All observations agree, as much of them were carried out recently, that granite is the lowermost kind of mountain on our earth, that all the rest are found on or beside it, it itself in contrast is not overlay by nothing else, so it, even if it not compose the entire earth, its nevertheless compose the lowermost crust that is accessible to us."
The Neptunism seemed well established by the observations in the field - in 1788 Werner publishes his work "Bekanntmachungen einer von ihm am Scherbenberger Hügel über die Entstehung des Basalts gemachte Entdeckung" (Notes about a discovery at the hill of Scherbenberg about the formation of basalt), where he describes the transition of sand, argillaceous deposits, conglomerate to basalt. The apparent horizontal bedding of the basaltic plateaus and under- and overlying sediments in central Europe was considered by Werner as a proof of the sedimentary origin of these rocks, unfortunately he never visited and observed active volcanoes.
An alternative, even contrasting theory to Werner´s Neptunism was proposed by the English naturalist James Hutton: primordial rocks, and their exposure, are due the effect of magmatic intrusions and eruptions. This theory was named after the Roman god of the underworld Plutonism. The resulting conflict divided geologist and an intense research begun to solve the riddle of rock formation.
In 1806 the Italian mining engineer Count Giuseppe Marzari-Pencati begun, in his role as supervisor of mines, to study the geology of Tyrol.
Fig.2. Count Giuseppe Marzari-Pencati.
Fig.3. Magmatic dikes ("Serpentinite") cutting trough marbles ("modified limestone"), the last also in contact with a magmatic intrusion of "granite" - as seen by a geologist in 1848 (figure from Geo-Mineralogische Skizzen über einige Täler Tirols).
Fig.4. And magmatic dikes of the Ladinian (228-237Ma) cutting trough marbles (former reef limestone), as seen at the locality of Mountain of Dos Capel, Dolomites, near Predazzo.
Based on his studies of the flank of the mountain of Canzoccoli, at the village of Predazzo in the Fassa Valley (Dolomites), he recognized the superimposition of granitic rocks onto sedimentary marbles - a geological impossibility for the geological concepts at these times. In 1820 Pencati publishes his observations in the journal "Nuovo Osservatore Veneziano.", his article will cause a lot of agitation between the European geologists....