March 30, 1759 (a Friday)

A series of rock formations that Arduino categorized as "primary" and "secondary".

A series of rock formations that Arduino categorized as “primary” and “secondary”.

On this date, the Italian geologist Giovanni Arduino (1714-1795) wrote a letter to Professor A.Vallisneri the younger, in which Arduino proposed a classification of Earth’s surface rocks according to four brackets of successively younger orders: Primary, Secondary, Tertiary and Quaternary. Today, his Primary corresponds to the Precambrian and Paleozoic Era combined, his Secondary is the Mesozoic Era, and his Tertiary and Quaternary combine to form the Cenozoic Era.

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