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.
In 1759, Arduino proposed a scheme that categorized rocks from the southern Alps into four groups. These were (in addition to the Volcanic or Quaternary series) as follows: the Primary series, which comprised schists from the mountain's core; the Secondary series, consisting of hard sedimentary rocks on the mountain flanks; and the Tertiary series, comprising less hardened sedimentary rocks in the foothills.