Vijlener Forest

The Vijlener Forest is located on a plateau between Vijlen, Cottessen, and Vaals and is one of the hotspots in the Ardennes. The area, some 280 metres above sea level, is one of the northern reaches of the Belgian Ardennes. Limestones from the Late Cretaceous lay on the surface here for millions of years. During that period, a lot of limestone was dissolved in rainwater. There are various hiking routes in the Vijlener Forest. A visit to this hotspot will teach you more about the oldest weathered soils in the Netherlands.

To see at Vijlener Forest

The dense Vijlener Forest conceals much of what can be seen here. The sea regularly inundated this area after the Cretaceous as well. Sand was deposited on the seabed, which later petrified. Later erosion of the sandstone formed irregularly shaped sandstone blocks. Staatsbosbeheer (the Forestry Commission) placed several of these blocks together as a geological monument called ‘Sandstone Blocks’ (Zandsteenblokken). The nearby ‘Zeven Wegen’ (Seven Roads) geological monument offers insight into the sediment left behind after the Cretaceous limestone dissolved. This dissolution process caused deep dissolution sinkholes (organ pipes) in the limestone under the Vijlener Forest, which are visible on the surface as saucer-shaped depressions called dolines.

Irregular sandstone blocks as silent witnesses of the sea.

Hiking trails and sights in and around the Vijlener Forest

Geological monument ‘Sandstone Blocks’ can be reached via a wooden bridge over the ditch and a short forest path. The sandstone blocks here have been collected from the surrounding area. They are each half to one and a half metres in diameter. Up close, you can see their fine-grained texture. Can you find fossils from the sea or sedimentary structures?

Geological monument ‘Seven Roads’ consists of a small abandoned roadside quarry. It is estimated that penetrating- rainwater dissolved 50 metres of limestone here over time. Only the insoluble components remained: flint, loam, and sand. If you are lucky, you may find the petrified fossil of a sea urchin.

Many hiking trails criss-cross the Vijlener Forest. Take a stroll through the forest and marvel at the number of dolines and their size.

An information board explaining the origin of the sandstone blocks.

Practical information

Geology in brief

The Vijlener Forest area gives you an impression of the weathering of rocks under the influence of time and rainwater. Here, the limestone of the Late Cretaceous and the sandstone of the first part of the Cenozoic have been transformed by dissolution and erosion into a thick weathered layer, with scattered loose pieces of sandstone.

Detailed photo that shows the quartz grains of the sandstone.

Geological structure

In the Late Cretaceous (76-66 million years ago), limestone of the Gulpen Formation was deposited in a shallow sea here. In the tens of millions of years that followed, the area alternated between a shallow sea and a river delta, in which sand and clay were deposited. About ten million years ago, tectonic forces raised the area, and South Limburg became permanent land. The (sub)tropical climate caused strong soil formation, as a result layers of sand changed into sandstone through cementing with silicic acid. Subsequent erosion washed away the unpetrified sand, leaving the sandstone blocks. As rainwater percolated through the soil for millions of years, the Cretaceous limestone dissolved, leaving non-soluble particles in a package called flint eluvium.

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