The country, as mentioned, slopes down from the mediocre elevations that occupy the SE. (maximum height, the Botrange ridge, 692 m.) to the low alluvial plains of the NO.
According to toppharmacyschools, the two parts are geologically different. What we can say the elevated part (over 100 m.) Is made up of lands which fall together in the primary and secondary series that are so widely represented starting from northern France, up to the heart of Germany. In fact, the massif, which for the Belgian part, as well as for the immediately contiguous French part, is usually called the Ardennes massif, is nothing more than the western continuation of the Rhenish schist massif, and is, like this one, the largely worn residue of an ancient block of corrugated chains, in which little or very nearly all the assizes of the primary age are represented, from the Siluric to the various planes of the Devonico and the Carbonico. The latter in particular s’ it inserts in thin strips in the northern slopes of the Ardennes descending towards the Sambre and the Meuse, since the carbonic limestone rests, below, on the devonic shales and in turn is dominated by the productive formation of the hard coal with the two large deposits of Mons (Sambre) and Liège (Meuse). Above the carbon then they appear, but only in the extreme SE. of the Belgian country, the Triassic and the Jurassic, while in the remaining Ardennes area, which emerged for a long time after the Carbonic, the secondary age is represented only by the Cretaceous. To these periods therefore belong the lands that make up the upper part of Belgium (up to N. della Meuse), which, having long since lost all traces of the original corrugation in the external forms, appear superficially as a series of vast uniform extensions, just varied from large depressions slightly hinted at, where the waters often putrid without drainage. Generally barren and sad lands, clothed with forests or monotonous moors: the area of the Hautes Fagnes (extended into the Hohe Venn) bordering the German land of the Eifel is particularly squalid, all peat bogs and ponds. Only the unequal resistance of the rocks gives rise here and there on the surface to the alternation of long, differently elevated or depressed areas; but real interruption to the uniform regularity of the landscape occurs only in the deep valleys that the major rivers have dug through the plateau (the Mdares to 87 m. of alt. a Dinant, 55 in Liège), depressions that the meeting of carbonic limestones makes particularly uneven and picturesque. Here and there in the limestones (both in these of the Carbonic and in the devonic medî) the karst phenomenon develops: thousands of chamoirs, aiguigeois, bétoires open their superficial foramina, while sinkholes and caves of superb beauty drill deep into the rock.
With different aspects from the monotonous Ardennes platform, the area of the Triassic and Jurassic “coasts” on the border of Luxembourg (in the so-called Belgian Lorraine) appears auche, much more broken and varied thanks to the frequent alternations of the limestone sandstones with the areas of marl and sand.
Starting approximately from the isoipsa line of m. 100 N. current of the great Sambre-Meuse furrow, the surface of the Belgian plateau changes character, declining with very slow hilly undulations towards the lowlands area. The changed character depends on the fact that here the surface soil is no longer formed by ancient rocks, which only still appear in the open in some valley incisions, but on the whole country (Hesbaye, Brabant, Northern Hainaut) a large uniform blanket of clays and sands: tertiary clays often passing through marl, sandstone, boulder, Quaternary sands which, accumulated here by wind action at the end of the great glacial expansion, are cemented in a fertile silt. This limo (limon), superimposed on the other assizes, forms a heavy and slippery soil after the rain, dry and cracked with dry weather, of exceptional agricultural value, alternating with areas of woods, where the soil is less favorable.
At the foot of this hilly area, the center and heart of the Belgian country, is the area of the lowlands. Such, in N., between the lower courses of the Schelde and the Meuse, passing between Belgium and Holland, the ungrateful land of Campine, a fragment of the primitive Rhenish delta terrace all sandy and gravelly floods, unfortunately resting on a waterproof iron conglomerate. The inability of the soil to feed plants with deep roots and to absorb the waters underground means that the landscape is mostly of arid dunes, moorlands, motionless marshes.
Also in the lowlands area, but to the west towards the sea, lies the country of Flanders, also entirely formed by recent floods and lying on a plain which, except for the surviving sandy hills from Cassel to Mont des Cats (m. 175), appears as flat and level as possible: sand soil, also naturally sterile, but reduced to productivity by the work of man, who has mixed the sub-lying clays with the surface sands and has in every way enriched and fertilized.
The last strip of the plain is finally the littoral area, resulting from river manure, peat deposits, marine clays: unstable transition between land and sea, always in the process of advancing pushing back the sea, always in the process of being depressed, offering room for marine incursions. The naturally raised belt of the dunes forms the extreme edge of this area, up to 30 m high in Coxyde, up to 1500 m wide in Knocke, interspersed with small depressions of damp pannes and dense shrubs. Behind them and protected by them (the dunes of the Belgian coast are a much more continuous bastion than those of Holland) are hollowed out the lowlands below the level of high tides, which only through the assiduous work of man have come freeing from the widespread stagnation of the waters.