Clay has been the raw material for the production of pottery since prehistoric times. Very often ancient human settlements arose near natural clay outcrops. This choice was useful both for the production of commonly used ceramic objects and for the possibility of trade with other populations. Unlike other much scarcer mineral resources, such as obsidian or flint, clay is found more frequently. But what is the geological origin of clay?

ORIGIN OF CLAYS 

There are clays that were formed by argillification, that is, physical-chemical alteration of other rocks, e.g., volcanic lavas, in the same place where they are still found today, or not far away. On the other hand, there are clays that after formation have traveled along with other sediments, transported by waterways to the sea, a lagoon or a lake; then fine particles were deposited on the bottom, stratifying. It is a common experience among potters that clay particles tend to remain in suspension for a long time, due to their electrostatic properties and low specific gravity, and that they are deposited by gravity only after pebbles and sand. These clays then made a long, sometimes very long journey, to reach the sedimentation basin. They then returned to the dry land where we now find them, millions of years after their formation, driven by immense geological forces. These are the basin clays. Clays can also form abundant deposits along the course of rivers if the water transport energy suddenly decreases, such as during a lean period of the river following a major flood. These are the alluvial clays.

CLAYS AND HUMAN SETTLEMENTS

Italy is extremely rich in clay deposits, and Campania in particular is among the regions with the highest concentration of archaeological areas connected to ceramic production centers. Three types of clays are present in Campania: pyroclastic clays near volcanic areas, alluvial clays along the course of major rivers, and basin clays, the oldest, which constitute the most abundant deposits. Looking at the map of Campania we can visualize a great quantity of archaeological sites, in the vicinity of each of which it is possible to identify an area of possible clay extraction for local needs, without prejudice to commercial interchanges with other cities for more valuable artifacts. These range from the prehistoric Gaudo culture in the Sorrento Peninsula to ancient Caudium in Sannio. In Irpinia the clays of the Ufita and Ofanto valleys are connected to the workshops of Calitri and Ariano, while in the Caserta area the Volturno valley deposits are connected to ancient Cales and the Piana del Monte Verna area. Also near Agropoli and Paestum and in the Velina locality, near ancient Elea/Velia, there are small outcrops and traces of ancient furnaces. On the island of Ischia there are deposits that have been exploited since ancient times. (1)

FRATTE ETRUSCAN TOWN

A very short distance from Salerno, at Fratte, there arose an early Etruscan and later Samnite settlement (perhaps the ancient Irnthi), between the late 6th century BC and the 3rd century BC. It rose near a navigable bend in the Irno River that connected it with the sea. It was part of the Etruscan colonies of southern Italy along with Pontecagnano and Capua and maintained constant relations with the mother country. It probably also owed its fortune to the abundant deposits of good-quality clay that could be found nearby. In fact, as many as two circular kilns and tanks for decanting clay have been found at the site, along with numerous tools, such as presses, smoothers, kiln spacers, bellows, as well as numerous firing scraps. All of this testifies to the presence of the different stages of ceramic processing, from the clay purification cycle to the firing of the objects. The site can be visited in part, and artifacts from the ancient settlement, acropolis, and numerous tombs form a rich collection on display at the Salerno Provincial Archaeological Museum. According to ref.(2), "of considerable interest is the discovery, during excavations in the 1950s, of a kiln, which together with the considerable number of matrices, spacers and clay smoothers, attests to the presence of a local ceramic craft activity."   

THE SALERNO CLAYS

Let us now examine the basinal clay deposit located near Salerno: it is part of the geological formation of the "Salerno Clays and Silty Clays." The succession of such clayey rocks "was deposited in a marine environment at first moderately deep and with normal salinity and later characterized by shallower depth, higher salinity and more restricted water circulation with at times conditions of partial isolation (lake-sea facies") (3). The age of the deposits, inferred from the microfossils present, ranges from 5.3 to 11.6 Million years (Tortonian-Lower Messinian, Miocene period of the Tertiary era).

The aforementioned clays outcropped on the surface, so they can be seen in several places: at Ceramiche D'Agostino and Il Casone, 1 km east of Brignano, a hamlet of Salerno, and in currently disused quarries located near Montecorvino Rovella. In Brignano a small lake, called "u fuosso ra creta," was formed by accumulation of rainwater inside the quarry used in the past by the D'Agostino pottery factory. These deposits, certainly exploited by the Etruscans of Fratte, but probably also in earlier times, are still used for the production of handmade terracotta tiles by the De Martino company in Rufoli. The nearby town of Vietri sul mare, a well-known ceramic city, also used raw material from these quarries in the past: transport of both clay and finished products for export was by sea.     

Bibliographical references

A. De Bonis, PhD thesis in Petrography and Petrology, Universities of Catania and Naples, 2010 (1) ⁽¹⁾

ISPRA Geological Survey, Illustrative notes Geological map of Italy, sheet 467 Salerno, 2010 (3) ⁽³⁾

M. Romito, L'Area Archeologica Etrusco Sannitica di Fratte, Provincia di Salerno - Settore Beni Culturali, Salerno 1989 ⁽²⁾