A flowering of research into the natural environment and particularly geology took place in Italy in the eighteenth century. New concepts of the composition and formation of mountains and the structure of the Earth arose from regional field investigation of the lithology and palaeontology of the rocks, geomorphology and their relative position. Classification of mountains and the rocks from which they were formed developed rapidly following the critical insights into basic geological foundation principles by the Florentine scientist N. Steno. From this classification, a broad system of stratigraphical sequence gradually emerged in the form of a relative chronology based on the position and relative properties of the rocks. This led to the proposal of the terms "primary" (or "primitive"), "secondary," and "tertiary" to describe the nature of mountains and in addition the terms began to be used as stratigraphic units. By the middle of the eighteenth century, the mining engineer and field geologist Giovanni Arduino, following two decades of fieldwork in the Venetian and Tuscan mountains, made a remarkable contribution when he proposed a classification of mountain and rocks in northern Italy. His scheme divided the mountains and rocks into four basic units or "ordini" which were based on lithology, position and internal structure, yet excluded fossil evidence. The three orders of mountains and a fourth of the plains, were respectively: "Primary" (underlain by "Primitive or Primaeval" schist considered to be the earliest rocks), "Secondary" and "Tertiary". His youngest division, the "Fourth Order" or "Quarto orate" comprised alluvial and estuarine deposits that underlie river valleys or plains. His recognition of the "Fourth Order" was the first time that deposits representing the Quaternary had been identified and defined as a discrete sequence. In this way, Arduino's classification system of divisions laid the foundations of modern stratigraphy.
