Giovanni Arduino

Giovanni Arduino was born in Italian poverty in 1714. He sought an education at Verona but found that reading books about the Earth didn't do him much good. Instead, he studied the Earth itself, making himself into an expert at mining and surveying. More than an expert in his own time, he made lasting contributions to geology.

From Earth's Deep History by Martin Rudwick

In the late 1750s, Arduino drafted a manuscript, a picture from which appears here. He never published it, but the tattered state of the manuscript — now kept at the Biblioteca Civica di Verona — suggests that he showed it to plenty of people. This illustration shows a series of rock formations that Arduino categorized as "primary" and "secondary," with an exaggerated vertical scale for clarity. Arduino's work expanded on the ideas of a Florentine naturalist, Giovanni Targioni Tozzzetti, who published a series of books proposing a two-category classification for Tuscan mountains. In 1774, Arduino finally published his own ideas. The classification system Arduino developed included these categories:

Primary or Primitive: These rocks usually fell at the bottom of the pile and usually had metallic ores but no fossils.
Secondary: These rocks included marbles and limestones, and were often tilted, i.e., they have been uplifted some time after they were deposited. These rocks contained fossils, but compared to what now lived on Earth, these fossils looked pretty weird. Arduino called them "unrefined and imperfect."
Tertiary: These rocks sat on top of the secondary (titled) layers and also contained fossils, and these fossils looked more recognizable. Arduino called these fossils "very perfect and wholly similar to those that are seen in the modern sea."
Quaternary: These were sands and gravels resting atop tertiary rocks.

Not surprisingly, many people who heard of Arduino's system forced it into a biblical chronology. Primary rocks, they concluded, must have been deposited right before Noah's Flood, and secondary rocks were obviously applied in the scant 40 days of the Deluge itself. But this was not Arduino's interpretation, even though he had been inspired by the work of Niels Stensen, who did relate his own work to the Bible.

In roughly two and a half centuries since Arduino proposed his classification system, it has seen only some modifications. Primary rock formations were later classified as Precambrian and Paleozoic. Secondary rock formations were later renamed Mesozoic. The names Tertiary and Quaternary survive in geology textbooks and papers to this day.

For more information:
The Seashell on the Mountaintop by Alan Cutler
The Birth and Development of the Geological Sciences by Frank Dawson Adams
Linnaeus in Italy edited by Beretta and Tosi
Song of the Earth by Elisabeth Ervin-Blankenheim
Bursting the Limits of Time by Martin Rudwick
Cultures of Natural History edited by Jardine, Secord and Spary
"The Role of the Mediterranean Region in the Development of Sedimentary Geology: A Historical Overview" by Fischer and Garrison in Sedimentology
Earth's Deep History by Martin Rudwick