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The Charmille de Haut-Marais (Haut-Marais hornbeam walk)

The Charmille de Haut-Marais owes its name to the neighbouring residence known as the "Château des Hauts Marais", which recalls the surname of the original owners of the place in the early 17th century. Simon de Marais, the Prince-Bishop of Liège's chief tax collector, acquired 20 bonniers of land in this area and had a house built there. Various great families followed him. After the Pierponts and the Borchgrave d'Alténas, the industrialist J.R. Nys settled there. He was responsible for the creation of the hornbeam walk in 1885. At that time it was much larger and led, in a "T" shape, from the house to the outbuildings and to the edge of the property. Three people could walk for a kilometre along it side by side. The hornbeam walk is supposed to be the longest in Europe; it is 573 metres long and 60 to 70% of its 4,700 hornbeams are a century old. It has been listed since 12 December 1979.

The Theux window

This is a distinctive and rare geomorphological and geological phenomenon. Over millions of years, the earth's crust created enormous folds and, during this time, one plate gradually pushed up and over another one. At the mercy of the weather, erosion slowly pierced a hole in the upper plate, thus making it possible to discover the formations of the lower plate.
Millions of years ago, Theux was the subject of a geological upheaval unique in Western Europe. Whereas from Ciney to Aix la Chapelle, all the geological strata are quite uniform and parallel to the Meuse, at Theux a tear occurred in the hard Ardennes soil, revealing older strata than the Condroz stratum - this is the Theux "Window".
Some people believe this was caused by erosion; others by an earth tremor. How else can we explain this erosion, over such a thickness (200 m) in this one, specific place, especially as there are no traces of eroded pebbles?
It is worth trying to give a simplified definition of the Theux "Window". In the vocabulary of earth sciences, a window is linked to the phenomenon of overthrust. An overthrust is the tectonic movement of a rock mass, called a sheet or allochthon, over another rock mass called the autochthon. This movement is predominantly horizontal. When erosion cuts an opening in the overthrust sheet and an outcrop of part of the autochthon is revealed, this part is known as a window. The phenomenon is continually evolving since the erosion of the formations is still ongoing. Consequently, the area of the window will inevitably keep on growing over time. Of course, this is not perceptible on the scale of a human life; it must be considered in terms of geological units of time.

Through this window, we can therefore see a succession of geological strata, and the stratigraphic series that can be seen shows few gaps.
Thus, within what used to be the enormous Ardenne Forest, which was not very suitable for agriculture, we find a landscape which is very unusual for the region: rounded hills and valleys cut through by the Hoëgne and its tributaries with long lines of ridges ("tiges") on the hard rocks, and hollows or "chavées" filled up in the bottoms by soft limestone.
Amongst other things, this last feature is responsible for the many and varied quarries providing stone for construction and road building especially at le Staneux, Timonheid, Spixhe, Franchimont, le Thuron, le Stockis, Chawieumont, Otmont Forest and Heid de Chaumont (for loose stones). The most famous are the two veins of limestone or extremely fine black marble (at le Wayot and Juslenville) which are therefore easy to work. They were worked and the stone exported for decoration and sometimes construction from the 2nd century until the start of the 19th century.
There are also sand pits at le Tillot and le Thier du Gibet, and rivers provide gravel.
In the valley areas, dust from rocks carried by the rain has accumulated, forming pockets of very fertile alluvium.
Within the "Window", and most often at the edge of it, carbon dioxide from the rain water has rapidly dissolved the limestone creating channels and tubes up which ores have risen as a result of volcanism.
  • limonite
  • calamine
  • blende
  • pyrite
  • galena

Lead and iron can also be found in the subsoil.

The Chafour

The name Chafour comes from "four à chaux" (lime kiln). There used to be a good number of these in the Theux region as there was little limestone elsewhere in Ardennes.  The Chafour is therefore an old quarry located right next to the village of La Reid. But it is also quite a special place where you can admire the phenomenon of "chantoirs" (cavities, chasms). These are places where a stream suddenly disappears underground before re-emerging sometimes much further on. In addition, here, the acid water of the stream attacked and hollowed out the limestone until the roof of the cave collapsed, producing a small canyon. The Association Theutoise pour l'Environnement (ATE or Theux Environment Association) has judged the site to be of sufficient interest to set up an information trail.