The formation consists of marine glauconiferous sands and clays that were deposited during the Miocene epoch.

Although the formation is not very rich in fossils, sometimes bones of fishes, mammals (Leptophoca cf.

proxima, Protophocaena minima),[1] shells and shark teeth (a.o of megalodon) are found.

The Breda Formation was deposited in the shallow sea that covered the Netherlands during the Miocene.

The Breda Formation can be a couple of meters (in the Roerdal Graben) to more than 700 metres (2,300 ft) thick.