The three regions may be grouped together as the Ardennes and its foreland. This low mountain region, or old plateau, belongs to the ancient Hercynian system. After being eroded to a peneplain in the course of tens of millions of years, it was uplifted during the Alpine period. Its highest elevations, reaching some 2,000 feet, are found in the east, and the plateau slopes down towards the northwest with a somewhat abrupt drop of 300 to 700 feet between the real Ardennes and the Ardennes foreland or Condroz region. The northward continuation of the Ardennes block lies buried under the young deposits and loamy soil of the central Belgian uplands. The rivers generally follow the inclination of the old peneplain, as the Meuse River which has eroded a narrow valley running northward till it reaches the soft coal layers outside the plateau, where it turns toward the east.
The Ardennes presents a strong contrast to the loamy upland in many respects. The Condroz foreland is, indeed, fairly productive, especially where it consists of limestone. There it supports rye, oats, and potatoes as the main crops, as well as considerable livestock, mostly dairy herds. But parts of it are covered with forest, and there the density of population is far less than on the loamy upland. The high part of the Ardennes with their oak forests and moorlands, where sheep-raising was formerly the chief rural industry, is still Belgium's least-developed region. Even here there has been a rapid change. Forests still cover great areas (about a quarter of the region), but the number of sheep has declined and on every hand are meadows and fields of rye, oats, potatoes, and forage crops; cattleraising, too, is gaining in importance.
The climate of the Ardennes, including the part in Luxembourg, shows the influence of high elevation as well as of increased distance from the sea. The higher parts have cold raw winters; the depressions have fairly warm and rather dry summers.
The small southwestern section of Belgium belonging to the limestone region of the Lorraine escarpment is mainly devoted to rye and oats, but does not show the intensive cultivation of the western regions. Luxembourg can be divided into two sections: the northern part, belonging to the Ardennes upland, produces little and is mostly forest land; the southern section, along the Lorraine escarpment, has fertile soils where oats, rye, and potatoes are abundantly grown, and even grapes can ripen.