The abandoned limestone quarry Falkenberg
Under a thin blanket of younger unconsolidated sediments, the landscape around Hochheim, Flörsheim and Wicker is composed of clays and clay marls that were deposited in the Tertiary Sea of the Mainz Basin during the Oligocene (around 30 million years ago). At the end of the Oligocene (around 24 million years ago) the sea returned and the sediments changed to limestone and calcareous marls. The hard limestone outcrops are characteristic feature of the landscape just like here on the Falkenberg.
Near Falkenberg, the limestone was downfaulted and therefore protected against erosion, while it has been nearly completely eroded in the surrounding area. The company Dyckerhoff AG began extracting the limestone in 1911.
The limestone contains numerous fossil snail shells belonging to the species Cerithium. Together with other fossils they indicate that the limestone was deposited in moderately saline waters (brackish water). Because of the predominance of snail fossils these layers were known for a long time as Cerithia beds.
Algae reefs
In addition to the layered limestone, one can also find massive limestone rocks with a cauliflower-like surface.
These are algae reefs. They are formed by cyanobacteria (blue-green algae), which trap sedimentary grains in their slime. This requires a high flow potential, which was found near the steep slopes of the Upper Rhine Rift. Similar algae reefs can still be found in Western Australia (Shark Bay) and the Bahamas.
Terrestrial snails
Caverns in the algae reefs provided excellent conditions for the preservation of terrestrial snail shells. Already in the 19th century this quarry was famous for the rich terrestrial snail fauna. Close to 100 different species were identified here, so many that the algae reef limestone of Hochheim was known as "terrestrial snail limestone"
In contrast to the brackish water snails, the terrestrial snails did not live here, but were swept up by rivers from the nearby coast and deposited here. In the mean time, the quarry has been acknowledged as the type locality for these strata, now called the "Hochheim Formation".