Cretaceous Walk on Mount Saint Peter

Due to marl quarrying, the continuation of the former Luikerweg has disappeared. The viewing platform symbolises this vanished road in the present day. From the platform, you can look out over the quarry and the small lakes with their deep azure-blue colour, caused by the reflection of the sky in the clear water. The deepest point of the quarry lies 5 metres below sea level, whilst the Meuse here lies 45 metres above sea level.

The quarry was created as a result of marl extraction by the ENCI (Eerste Nederlandse Cement Industrie). From 1926 onwards, calcareous marl was quarried in the heart of the Mount Saint Peter for the cement industry. Every year, 900,000 tonnes of cement were produced here, and the striking chimney of the ENCI factory still towers high above the landscape. In 2018, ENCI ceased marl extraction, after which Natuurmonumenten took over management of the area in 2020. Thanks to this takeover, nature was once again given the space to flourish here, and the area was transformed into a nature reserve.

In the quarry you can see islands; these mark the sites where Mosasaurus remains were found. Over the years, four have been found: Bèr, Carlo, Kristine and Lars, all named after the people who discovered them. The rock layer in which these mosasaurs were found is called the Maastrichtian. This geological layer was named after the city of Maastricht in 1849 by the Belgian geologist Dumont.

At the end of the Cretaceous Period, some 65 to 75 million years ago, marlstone was formed. At that time, the area was covered by a warm, shallow sea. The skeletons of many small creatures that lived in this sea sank to the seabed and, over time, were buried under silt and sand. This eventually gave rise to the type of rock we now call marl.

Marl has a high chalk content, and white marl consists of almost 100 per cent limestone. The more orange-coloured pieces contain iron and other minerals as well as limestone. You can still find plenty of fossils in the marl, such as shells, mussels, shark teeth, sea urchins and squid arrowheads.

Flint is the hardest type of rock found in the Netherlands. Along the footpath, you can clearly see different layers of flint. A fault line, where the layers no longer run straight, indicates an ancient landslide. The exact origin of flint is still not fully understood. It is likely that the Cretaceous Sea occasionally dried up, leading to the growth of plants and trees. Crustaceans also burrowed tunnels through the soil.

After the Cretaceous period, the Ardennes mountain range formed, causing the ancient Meuse to flow more rapidly. This led to increased erosion and the transport of material, such as gravel and silt. The acidic gravel slowly seeped through the marl layer, filling the cavities and passages left behind. In the flint layer, you can often make out a root or branch-like structure.

You are now standing on the Zandhoek, the upper part of the dry valley, also known as the Poppelmondedal . At the top, the soil is poor, consisting mainly of herbs and very little grass. In the limestone-rich section below, (very) rare plants such as limestone saxifrage grow. You’ll also find orchids, ground elder, wild marjoram and rock thyme. These herbs attract various species of butterfly, such as the Spanish Flag, the Queen’s Page and the fringed Aurelia.

From this western slope, you can once again enjoy a magnificent view over the Jekerdal. On the opposite side, to the left on the slope, lies the Apostelhoeve, the Netherlands’ first commercial vineyard (1970). The vineyards belong partly to the Apostelhoeve and partly to the Nekummerhoeve. Vineyards have been here from Roman times right up to the 17th century. The limestone soil provides excellent conditions for growing grapes. This is why, historically, many vineyards in Europe have been established on limestone or calcareous soils.

Be sure to check out the Explore Maastricht blog too

From the Kiekoet , you can enjoy views over the Eagle Owl Valley, home to Europe’s largest owl. This impressive bird can grow up to 75 centimetres in length and has a wingspan of no less than 1.80 metres. A pair of eagle owls has been nesting here successfully since 1998. The eagle owl needs a peaceful nesting site, with as little human disturbance as possible, sufficient food and a steep cliff face on which to nest. These owls have a large territory and hunt pigeons and rats at night in the city of Maastricht.

In 1673, Maastricht was besieged by Louis XIV, the Sun King. After the Netherlands regained control of the city, Stadtholder William III had Fort Sint Pieter built in 1701 to protect the city from attacks from the south. The fort was last used during the Belgian secession. After 1867, it lost its military function and fell into disrepair, being used, amongst other things, as a warehouse, a stable and a ‘quarry’. During the Second World War, the fort served as an air-raid lookout post, the concrete structure of which is still visible. The fort was restored between 2007 and 2014. Inside the fort, there is an underground spiral staircase running alongside the well, which provides access to a chamber connecting to the Northern Corridor System.