The scheme proposed by Arduino in 1759, which was based on much study of rocks of the southern Alps, grouped the rocks into four series. These were (in addition to the Volcanic or Quaternary) as follows: the Primary series, which consisted of schists from the core of the mountains; the Secondary, which consisted of the hard sedimentary rocks on the mountain flanks; and the Tertiary, which consisted of the less hardened sedimentary rocks of the foothills.
Arduino's rock classification scheme of 1759 was based on his study of rocks found in the southern Alps, which he divided into four groups: the Volcanic or Quaternary series, the Primary series (schists from the mountain's core), the Secondary series (hard sedimentary rocks on the flanks), and the Tertiary series (less hardened sedimentary rocks in the foothills).