The "classification" of mountains in eighteenth century Italy and the lithostratigraphical theory of Giovanni Arduino (1714-1795)

During the 18th century, scientific literature devoted to the Earth sciences documented a significant increase in the study of the composition and formation of mountains and above all their stratigraphical sequence. The diverse and widely ranging philosophical theories of the late 17th century on the origin of the Earth were gradually replaced by new concepts based on field research on both a local and regional scale. This new approach analyzed the lithology and the fossil content of the rocks, the geomorphology of the area and in some cases helped to determine the chronological sequence of mountain formation. Nicolaus Steno's idea of superimposition of strata (1667-69) was followed by most of the late 18th century scholars in Earth sciences, who developed sub-divisions of mountains from the point of view of their formation, but which also included a classification of the rocks. These sub-divisions supported the idea of relative chronology of the formation sequence of the studied strata: the most recent or the most ancient formation could be deduced from their position in the sequence but also from their external lithological features. In this context the role of scientific terminology, which was gradually established in 18th century geological science, became very important: the terms "primary" (or “primitive”), "secondary" and "tertiary" were used for indicating the categories of mountains but also for stratigraphical units. In the second half of the 18th century, the work of Giovanni Arduino contributed decisively to the development of basic lithostratigraphic ‘classification’ of rocks and mountain building. His lithological studies, a result of twenty years of fieldwork in the mountains and hills of the Venetian and Tuscan regions, were also supported by a specialized knowledge in mining. The new ‘classification’ into four basic units called "ordini" (1760) was based only on lithology (without using paleontological indicators) and included different rock types which formed three kinds of mountains and one kind of plains in a regular chronological order: "Primary" (underlain by “primeval” schist considered by him to be the oldest rock type), "Secondary" and "Tertiary". A “fourth” and younger lithological unit included only alluvial deposits. Arduino's system is still regarded by the geological world as being one of the starting points for modern stratigraphy.