The Limburg basin, which measures about 20 by 14 kilometres across and is almost treeless, is a tectonic intrusion field (
Einbruchsfeld) and connects the more deeply incised valley sections in the Weilburg Lahn Valley area with those of the Lower Lahn Valley. It is divided into the North and South Limburg Basin Hills and the almost level Inner Limburg Basin, including the
Villmar Bay and Linter Plateau, in whose bottom the winding course of the course of the Lahn has sunk about 50 metres deep. The hills that rise at the edges of the basin or within it form landmarks that are visible from a long distance away, dominating the landscape. These include the
Heidenhäuschen () north of
Steinbach, the
Mensfelder Kopf (313.7 m) and the hill ridge of
Galgenberg (up to 277.1 m) on the far side of the eastern rim of the basin in the Langhecken Lahn Taunus (in the
Eastern Hintertaunus) near
Villmar. The bedrock consists mainly of rocks from the geological
Lahn Depression, which outcrop at the edges and on the steep slopes of the valleys. Of particular importance here are three beds of Middle
Devonian Corallian Limestone (
Lahn Marble) which are embedded in the predominantly volcanic rocks (
diabase,
schalstein) of the Lahn Depression. In the north, the terrain is shaped by the younger
volcanism of the
Westerwald with individual
basalt deposits - the
Galgenberg () at
Hadamar, the Großer Berg (}) at
Ahlbach, the
Beselicher Kopf (}) at
Obertiefenbach. These are related to tectonic distortions, which pass through the basin in a north–south direction and are recognizable by the
Weitungen at
Dietkirchen and Limburg as well as by ditch fillings (sand, gravel, clay). The Lahn leaves the basin at the
Diezer Pforte and transitions, accompanied by a flight of terraces, into the Lower Lahn Valley near
Fachingen. The
mineral springs there rise from a tectonic fault line, which forms the western rim of the basin facing the
Western Hintertaunus, the line is discernible from the
thermal springs of
Bad Schwalbach and
Schlangenbad running up to the
Rheingau. Large areas of the Limburg Basin are covered by thick
loess layers, for example, on the
Ahlbacher Bördenplatte which is flanked by the
Elz-
Hadamar Basin Rim with the
Elbbach bottom and the
Schupbach-
Hofen Perimeter Plateau with the valley of the lower
Kerkerbach as its boundary. The
black earth-like soils, together with the favourable climate of the basin, have resulted in an important old settlement area with intensive corn and
root crop farming. In the southern part of the basin, the
Kirberg Hills, the local name of "Golden County" (
Goldene Grafschaft) on the
Aar and the
Goldener Grund along the
Emsbach reflects the fertility of the area. Not to be underestimated is the historical importance of the basin for road communications as there is a key crossing over the Lahn at Limburg, used by long-distance trading routes of the early Middle Ages. The
A3 motorway and
Cologne–Rhine/Main high speed railway continue this tradition by following a very similar course. == Sources ==