The beach of the marine corner is geologically based on the so-called “formation of Valongo”, composed lithologically by mica- schists, from the Paleozoic era, framed in the period of the Ordovícico that dates from between 478 and 458 million years. It was on these rocks that in an interval of time, which may have elapsed between the Iron Age and the Romanization of the territory, the salt marshes that constitute the object of the present study were carved.