Geology for you

Heimans Quarry

In the Geul Valley in South Limburg, just before the Belgian border at Cottessen, you’ll find the oldest rocks that occur on the surface in the Netherlands. The rocks are located in the now abandoned Heimans Quarry. The fossilised sediment was deposited between 326 and 313 million years ago, during the Namurian, a period of the Carboniferous. The quarry is named after the Amsterdam naturalist and educator Eli Heimans.

Historical photograph showing workers in Heimans Quarry in southern Limburg.

To see at the Heimans Quarry

The Heimans Quarry is a geological monument managed by foundation Het Limburgs Landschap. In the quarry, you can observe petrified layers of clay (shale) and sand (sandstone). Once there was a shallow sea here in which sand and clay settled. Waves on the surface of the water stirred the seabed. Over the course of geological history, clay and sand were buried more deeply and became petrified. Tectonic forces caused the rock layers to fold and become slanted. Careful observers can see wave-formed ripples and the fossils of plants and marine animals.

Sandstone and shale in the Heimans Quarry.

Hiking routes and sights at the Heimans Quarry

You can enter Heimans Quarry and take a closer look at the rocks. With some luck, you will find ancient imprints of plants and shells, or wave-formed ripples, like on the beach. The chances of finding plant fossils are especially high in the darker rocks. Do you recognise the curved shape of the rock layers resulting from tectonic folding? For additional information, there is an information board at the quarry. A little further south along the river Geul lies Cottesser Quarry with quartzite banks of the same age as those in the Heimans Quarry. There is also an information board there.

Information board Heimans Quarry showing slanted rock layers.

Practical information

Geology in brief

When there was a shallow sea here, the Netherlands was a few degrees latitudes south of the equator. Advancing orogeny (the building of mountains) from the south made the shallow sea increasingly smaller. Rivers transported sediment from the mountains towards the sea, carrying all kinds of land plant remains with them.

Blue-grey shale with cracks.

Geological structure

The Carboniferous era in southern Limburg developed against the backdrop of northward-shifting mountain building, the Variscan mountain building. At the start of the Carboniferous era, thick layers of limestone formed in a sea, remnants of which can still be seen along the motorway near Visé in Wallonia. Partly due to the advancing mountain building, the sea became smaller over time. The deposition of  limestone  was followed by the deposition of clay and sand in rivers, seas, and swamps. The rock in the Heimans Quarry is part of this large-scale land accretion. The final stage of this process was the formation of expansive peat bogs. After millions of years and under the influence of high pressures and temperature, the peat was transformed into coal, which was mined for decades in the area between Geleen and Kerkrade.