The Saarland is a basin, in the geologic sense a syncline, the downbent part of a huge wave-like deformation of the crust. The whole area was in a continuous subsidence during a certain period of time called the variszian orogeny. The synclinale and the bordering ridges run in northeast-southwest direction. The northern ridge is the geologic structure of Rhenoherzynikum, the landscape is called Hunsrück. The southern border is the Saxothuringikum which is formed by the Pfälzer Wald.
This basin and ridge structure is crossing the whole central Europe. It starts in the east with Harz-Thüringer Becken-Thüringer Wald and ends in the west with Ardennes-Paris Basin-Vosges. The basin ends in the area of Paris.
The central basin was a sedimentation area during the Middle and Upper Devon, whenn shallow water limestone was deposited. This limestone covers the basin in mighty layers. But as this is a basin, there is no drainage and thus no baseflow and no karstification. Only at the northern rim, where the Hunsrück ridge forces the limestone layers up, they are a little karstified.
The basin was formed mainly during Upper Devon and Lower Carbon. At this time the basin was continually subsided, but also the northern and southern ridges where uplifted. The uplifted ridges were eroded, the material transported to the basin and so the deposited rocks of this time sandstones, conglomerates and silt. In the Carbon the area was covered by abundant forests, growing in warm climate and most of the time forming a huge swamp, where the wood did not rot, but formed huge layers of peat. This peat was covered by sandstone or conglomerates, and the next forest grew. In this periodic process during the Upper Carboniferous, numerous layers of biogene material were deposited, which were transformed into coal by pressure and heat.
The Upper Carbon coal formation in the basin is approximately 4,500 m thick and contains 150 coal leads with more than 60 cm size, which means about 190 m of mineable coal. This coal contains more ash and more gases than the coal from the Ruhr area nearby. It is used to produce coalite in a special coalite process.