The shale of Muehlwand was formed in the Paleozoic during the Silurian period. Most of life was still in the sea and the simplest of plants had only just begun to take over the land. What is Vogtland today was part of the ocean floor in the southern hemisphere around 430 million years ago. At that time there were 400 days with 22 hours per year. The climate was calm, warm and sunny. There was a shortage of oxygen in the sea due to the lack of storms. This caused metals such as iron and others dissolved in the water to flocculate and sink to the bottom. Nevertheless, numerous extraterrestrial life forms populated the sea, which also sank to the bottom after their death.
Paleozoic means 'time of ancient life', so it refers to the development of life and not to the age of the earth itself, which is about 4.6 billion years. The first biological structures are known from the middle of the Precambrian (~ 2.5 billion a). But life developed very slowly until it literally blossomed around 550 million years ago, at the beginning of the Paleozoic Era (called 'Cambrian explosion') . For the first time, an extensive and differentiated, albeit very strange animal and plant world emerged in the sea, which conquered the mainland by the middle of the epoch.
In the geotopes in and around Muehlwand, geological processes can be identified that have significantly shaped the current shape of the Vogtland and other landscapes. Most of the Vogtland strata and slate rock originated from marine sediments of the Ordovician (~ 480-445 million a). The Muehlwander alum shale, on the other hand, was formed from sediments of the Silurian period (~ 445-420 million a). And the diabase rock of the typical Huebel and Poehle comes from submarine volcanoes in the Devonian (~ 420-360 million a). In the following section of the Carboniferous (~ 360-300 million a), the orogenic forces by building the Varisks mountains caused massive folds, fractures and faults in the shale rocks.
Layer by layer, sediment formed on the sea floor from clayey mud, dead organisms and flocculated metals. The organisms, which decompose poorly due to the lack of oxygen, were partly turned into coal (carbonized). Partly their decay products had combined with the precipitated metals (so-called digested sludge facies). Over millions of years, the mud was convertet into black mudstone and than into clay slate with different phosphate and sulfide inclusions (apatite, pyrite, marcasite). In addition to the often colored minerals, fossils (traces of life) can also be found in the Muehlwander slate: above all gray-silvery remains of graptolites, less often physical prints (so of crinoids, 'sea lilies').
On some pieces of slate you can see strange, finely toothed lines, arcs, circles or forks: the graptolites. They are fossil remains of colonizing organisms a few centimeters long that have long since died out. Because their shapes changed again and again over time, their prints are very suitable as guide fossils to determine the age of the surrounding rock. The 'drawings' come from the rows of housings of the graceful little animals that once floated in the primeval sea. As a light mineral gumbelite, they stand out quite well on dark slate.
The actual, only ½ millimeter tiny animals lived in individual living chambers (counters) made of chitin and fetched plankton as food from the water with their tiny tentacles.
In the Silurian, the era of the mighty dinosaurs was still a long way off. Some of the most powerful hunters of the sea were huge scorpions: the Eurypterites. With their powerful claws they hunted mainly large cephalopods, nautiloids (top picture) or armored fishes and agnaths ('jawless', below), which were the most developed animals at that time.
The Silurian era was followed by the Devonian era (359 - 419 million years ago). In the middle of this period there were violent tectonic movements of the earth's crust, which resulted in numerous fractures and fault lines. The whole of today's Vogtland was divided into thresholds and troughs ('Reussian phase'). Magma rose along the fracture zones, poured over the sea floor or just below it. It also pushed itself between the sediment layers of earlier epochs and solidified there in the form of banks or flat lenses. So it is that today the Devonian volcanic rock diabase is found surrounded by slate millions of years older.
Diabase was once volcanic, dark gray basalt. The long lying in the sea water and strong earth forces turned the dark minerals it contained into green chlorides and serpentinite. As a result, the rock today shows a more or less greenish color in quarry and is therefore also called green stone. Diabase occurs as solid stone, as tuff or as slate, also under other names. However, the petrologically correct, albeit uncommon, name in German is Paläobasalt (paleo basalt).
The typical hills annd little peaks of the Vogtland - often called Huebel or Poehl - are mostly remnants of former marine volcanic cones from the Devonian period and consist of hard diabase, its tuff or rubble. They shape the landscape from the Burgstein area to Greiz (Schönfeld) and Zwickau (Schönfels).
Occasionally one also finds volcanic ejections formes from diabase: spindle-shaped or loaf-shaped, former lava 'bombs', with shell-like weathering due to the once rapid, radial cooling in the sea water.
In the following geological epoch of the Carboniferous (300 - 359 million years ago), mountain-forming forces pressed the rock layers together, which led to shifts, tilting and almost playful folds and loops in the rock. These unmistakable evidence of tectonic movements can be seen several times in Muehlwand on a scale from several meters to the centimeter range (folds and folds in larger folds).
⊕ Natural monument 'lying fold' and Variscan Mountains | show ⇓
+ Natural monument 'lying fold'
Another interesting natural monument is located about 100 meters from the visitor mine on Rotschauer Straße: the so-called 'lye fold'. In this fold of rock in the Ordovician 'main quartzite' (actually a mica- and sand-containing slate, approx. 540 million years old), which is almost 180 degrees overturned, the lower part of the older rock lies above the younger one.
+ The Variscan Mountains
The foldings in the carboniferous period was so powerful and extensive that the largest 'folds' were many kilometers wide. This created a wave-like high mountain range from France to Poland. Because of the approximately central city Hof in the Bavarian Vogtland (the curia variscorum = city of the Variskers) it's called Variscan Mountains, or Variscan for short..
By the end of the ancient world (252 million years ago) - at the beginning of the dinosaur age - the varisks had largely been removed. The landscape in the south of Central Germany today consists of its last remains or hulls. But the Variscan "giant folds" can still be read in the alternating saddles and hollows of the Thuringian Slate Mountains. The easternmost part of them represents our Goeltzsch vallye up to Lengenfeld. The peaks of the 'wave mountains' were particularly subject to erosion, so their hulls - called saddles - today only consist of the old Paleozoic rocks (Ordovician and older). In the former valleys and today's hollows, however, the younger strata (Silurian, Devonian, Carboniferous) have been preserved. At the respective transition zones from the Mulde to the Sattel and vice versa, relatively narrow outcrops of layers of middle Paleozoic age - such as that of alum shale - are therefore repeated at intervals of around 20-30 km. The vitriol and alum works were built around and after 1500 on these transition lines.
The locations of alum work plants former in Neumark, Muehlwand and Plauen are on the easternmost line. On the next line to the west, in Thuringia, the alum work plant Zeulenroda and on the next again the Saalfeld Feengrotten (fairy grottoes) and the pits near Schmiedefeld and Fischersdorf.
Farther to the east, in the area of today's Ore Mountains, it came through later renewed uplift and inclination of the Variscan hull landscape to increased weathering and erosion. There the Silurian alum slate and younger layers were completely lost. Therefore, today in the Ore Mountains - in addition to magmatic rocks of various ages - only the older deposit rocks are found, which are mostly tectonically strongly changed (metamorphically overprinted and often richly mineralized = Ore Mountains).
This is the complementary uniqueness of the Muehlwand geotope and visitor mine compared to the mining and world heritage region of the Ore Mountains and all of Saxony.
