The Fond des Vaulx

This is the tunnel that will take you the entrance of the Fond des Vaulx (see map). Justbefore the tunnel, at
the foot of the railway embankment, you will see a water flowing along a channel of embedded stones. This is a resurgence, through which emerges all the water from the Fond des Vaulx karst system that you will be retracing on this trail. This small valley, though which the Marchette stream runs, lies close to the town centre of Marche and covers an area of 25 hectares. Its steep valley sides and “untamed” character is in stark contrast to the expanses of the Marche plains. In addition to natural and geological attractions, this is a spot famed for the many legends and mysteries that make up the folklore of Marche. The Fond des Vaux is a picturesque valley, often presenting as a dry valley despite the presence of a river much further upstream. To understand how the water disappears, we need to look at the rocks beneath our feet. The valley is to a large extent carved out of Devonian limestones, shown in violet on the map, but originates on the sandstone plateau south of the locality of Agrismont. When the stream reaches the limestones, it plunges underground
through the swallow-holes frequently referred to as chantoirsin Walloon. The water then flows in the form of underground rivers until it returns to the surface via resurgences (karst springs). When swollen by heavy rainfall, the flow of water partially resumes its surface course. The system of underground cavities is known as karst. The cavities are the result of a long, slow process of dissolution of the rock over millions
of years, a process known as karstification.