The Taunus is geologically divided from south to north into the units Vordertaunus unit (also northern
phyllite zone or
metamorphic southern edge zone), Taunus ridge unit and Hintertaunus unit. Finally, south of the Lahn, the Taunus natural region has a share in the Lahn
trough and the
Giessen nappe.
Vordertaunus The Vordertaunus Unit is a narrow zone of weakly
metamorphic rocks such as
phyllites,
greenschists and
sericite gneisses. They are appear greenish through
chlorite and
epidote. The starting products of these rocks were
mudstones and
volcanic rocks. The rock strata occurring in the Vordertaunus are divided from north to south into the metavolcanic sequence, the Eppstein slate and the Lorsbach slate. The oldest
sedimentary rocks of the Taunus are the phyllites of
Bierstadt from the
Early Ordovician epoch, known only from a borehole in
Wiesbaden, with an age of about 480 million years determined by the evidence of
spores. The volcanic rocks of the metavulcanite unit are younger, they could be dated to the
Upper Ordovician and
Silurian using
uranium-lead dating. They are overlaid by the Eppstein slates of the Silurian and the
Lower Devonian Lorsbach slates. At the very southern edge and in a small deposit near
Mühlbach in the east of the Vordertaunus unit, limestones are exposed that are attributed to the
Middle Devonian.
Taunus crest To the north of the Vordertaunus is the Taunuscrest, also known as the High Taunus, which mainly consists of
Lower Devonian clastic rocks. It is composed of the
stratigraphic sequences
Graue Phyllite,
Bunte Schiefer,
Hermeskeilschichten and
Taunusquarzit. The Lower Devonian sub-layer only appears in two small outcrops, metavolcanites of the type found in the Anterior Taunus rocks. The
Graue Phyllite consist of
slates and
sandstones. They contain impressions of
Upper Silurian brachiopods and
corals and were deposited in
shallow water. The clay slates of the
Bunte Schiefer are greenish-grey or strikingly
violet in color due to finely distributed
hematite.
Agnaths (jawless fish) found in the
Bunte Schist are from the
Gedinne (Lochkovian); just like the formation of the
rock, they show a deposit of the colorful slate in
rivers or
lakes. The rocks of the colorful slate are found on the
Großer Feldberg, where they were mined in tunnels to extract roofing slate (slate tunnel below the
Red Cross).
Quartzite sandstones are embedded in them, from which the Brunhildis rock on the summit of the Großer Feldberg consists. The
Hermeskeil layers are exposed below the Großer Feldberg and consist of mudstones, weakly consolidated micaceous sandstones and quartzites of the Lower Siegen (Lower Pragian). They are covered by several 100 m thick layers of Taunus quartzite (Middle Siegen, Pragian/Emsian). The very weather-resistant rock forms many summits of the Taunus ridge (
Altkönig,
Kleiner Feldberg,
Glaskopf), but also individual rock elevations (such as the
Hohle Stein). The
Celtic ring walls and the rubble heap on the "
White Wall" on the Altkönig consist of Taunus quartzite. The fractured groundwater of the Taunus quartzite is of local interest for water extraction. They are dammed by the underlying
Hermeskeilschichten and pumped through groundwater tunnels. Four such groundwater tunnels make a significant contribution to Wiesbaden's water supply.
Hintertaunus The largest unit of the Taunus in terms of area, the Hintertaunus unit, is mainly composed of the black rock series of the
Hunsrück slate and the Singhofen layers of the lower Ems tier, often
greywacke-like sandstones as well as
siltstone and
claystone. Younger rocks are only exposed here in small occurrences near
Usingen and on the very eastern edge of the Hintertaunus in the
Oberkleen area. The geology of the Hintertaunus is not as well known as that of the Vortaunus and Hochtaunus in the south or that of the Lahnmulde in the north due to the often monotonous sandy and slate rocks that form only a few continuous reference
horizons and provide hardly any
index fossils. The Hunsrück slate refers to a
rock facies occurring mainly in the Hunsrück and Hintertaunus, which is composed of pure, mostly black mudstone and embedded sandstone banks and occurs in stratigraphically different positions in the Upper Siegen and in the Ems. The bulk of the Hunsrück Slate is attributed to the
Elm Lower Stage. It is known for its exceptionally well-preserved
fossils and is locally well suited for use as
roofing slate. In the western Hintertaunus, the almost sand-free Hunsrück slate can be easily separated from the sandy rocks of the Singhofen layers, in the east, rocks in the
facies of the Hunsrück slate recede. Transposed volcanic
tuffes and
ashes, the so-called
porphyroides, are integrated into the Singhofen layers, they can be traced in some cases over several tens of kilometers. The Middle Devonian to Lower Carboniferous of the
Usinger Mulde is only about 250 m thick and strongly tectonically disturbed, in the Lahnmulde and Dillmulde typical rocks of this time such as
Schalstein,
Massenkalk and
deck diabase absent here. The greywacke occurring here and at other places in the eastern Hintertaunus cannot or can hardly be distinguished from the
Carboniferous Kulm greywacke and are considered by some scientists to be the remains of the viewed
Giessen Ceiling. Due to its hardness, the Taunus quartzite was often mined in the past, currently only one quarry near Köppern is in operation. Some limestone and diabase quarries are still in operation in the part of the Lahnmulde that belongs to the Taunus. In addition, there are countless smaller quarries to supply the local population with building blocks. ==History==