Condroz

The Condroz is a textbook example of how geology (the rocks) determines the topography (the highs and lows) and land use. The Condroz consists of a rolling landscape in which elongated parallel ridges alternate with wide depressions, with a difference of about 50 m in height. The ridges are at about 300 meters, and the depressions at about 250 meters. The depressions correspond geologically to limestone from the Lower Carboniferous. And the ridges with sandstones or psammites from the Upper Devonian. This is remarkable in itself, as usually you find the older rocks (Upper Devonian) at the bottom and the younger ones (Lower Carboniferous) at the top. But here it is reversed. This happens because the limestone erodes faster than the harder sandstones (psammites). And due to the folding of the rock, the older sections protrude above. Geologists call this alternation of folds anticlines and synclines. Thus, the underlying anticlines of the sandstones from the Upper Devonian break through the synclines of the younger Lower Carboniferous.

Typical places where you encounter such a depression are in Natoye and Ciney. If you want to experience a beautiful succession of ridges and depressions, you should head NW or SE. For example, from Namur to Marche. The hills of hard sandstone are called tidges and the wide low areas, the 'chavées.' These low areas were carved out by erosion in the softer limestone layers. The rivers also follow the relief. In the chavées, small winding streams run that occasionally disappear into the limestone.

Pascal Brackman