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In the middle of the forest on the Antonshöhe (356 m) in Vienna-Mauer there is a flint quarry that is now protected as a natural monument and was discovered and researched in 1929. Radiolarites, which are rocks that consist almost entirely of silica (SiO2) and are therefore as sharp as glass, were mined in this quarry. The radiolarites from Antonshöhe have been used as raw material for tools since the fifth millennium BC, as prehistoric excavations prove.

The radiolarites formed more than 140 million years ago at a depth of several thousand meters from the bizarre shells of tiny marine unicellular organisms (radiolarians). The flint blades ("Steel of the Stone Age") from Antonshöhe can be seen today in Room XI in the Natural History Museum. Feuersteingasse is reminiscent of Vienna's early mining industry, which still supplied gravel in the 1930s.

Unique names, forgotten mines

Whether Tongasse in the 3rd district, Ziegelofengasse in the 4th and 5th districts, Lehmgasse in the 10th district, Steinbruchgasse in the 14th district or Sandgasse in the 19th district, street names are a first and direct indication of the geology of Vienna. The geological structure of the city can also be seen here: the solid rock deposits in the Vienna Woods area with the flysch zone (in the west) and the Northern Limestone Alps (in the southwest) and the loose rock (clay and sand) in the Vienna Basin with the extensive gravel terraces.

If you look at historical maps from the 19th and early 20th centuries, when Vienna was not yet so densely built up, you will find numerous raw material mining operations. Signatures and abbreviations such as S.G. for sand pit, Z.O. for brick kiln or Z.W. there are clear indications for brickworks. From the second half of the 19th century onwards, expanding Vienna had an enormous need for building raw materials (sand, gravel, clay). Due to its geologically favorable location in the Vienna Basin, it was not far from the numerous clay pits, where Tegel or loess was mined and burned into bricks on site, to the next construction site. Today, the former quarries have long since been shut down; they are mostly densely built-up; only in rare cases does the topography reveal something of the once massive interventions in the landscape.

Examples of this can be found on both sides of Triester Street in the 10th district, where the last brick kiln belonging to the Wienerberger company was shut down in the 1960s. What initially remained was a huge pit in the blue-gray Tegel, a deposit of the former Lake Pannon - a 290,000 km2 brackish lake that also covered the Vienna Basin eleven million years ago. The lake, hundreds of meters deep, was similar to the Caspian Sea and was home to rich and unique wildlife. The former brick pit soon filled with water and became the Wienerbergteich, which, covering 14 hectares, became a huge local recreation area in the south of Vienna.

The Roter Berg park in Ober St. Veit in Vienna-Hietzing would be another example. The Glasau quarry, which is located at the confluence of Jagdschlossgasse and Veitingergasse, became a wild landfill for building rubble after it was closed down in the 20th century before it was reclaimed by nature. In the 21st century, nothing can be seen of the rocks of the Jurassic period (Mezoozoic Age).

Another example of where an extensive raw material mining operation became a wonderfully designed recreational area is the Türkenschanzpark, which opened in 1888 with its ponds, playgrounds and botanical diversity in Vienna-Währing (18th district).

Finally, an example from Döbling (19th district): Along the Heiligenstädter Straße leading out of town, between Barawitzkagasse and Grinzinger Straße, there were once extensive brick pits where Tegel and loess were mined. The names of the former operators, Kreindl or Hauser, are now only known to a few people. There are now extensive residential complexes on the site.

Positive additional effects: knowledge gains for science

Enormous volumes were mined in the numerous clay and sand pits and quarries, and no one is surprised that attentive workers also found fossils. In most cases, science also found out about it, and in rare cases, workers tried to do business with it. It is no coincidence that the collections in the Natural History Museum, the Federal Geological Institute and the University of Vienna are now full of fossils. Today, the finds from the past still provide material for research work. New methods provide insights into Vienna's geological past. Epochs with subtropical climates as well as with ice age tundras are opening up before our eyes.

Let's stay with the brick pits on Heiligenstädter Straße, they were not only unusually rich in fossils, they also revealed layers of different ages. That's why the Kreindl Brickworks not only contains bones of seals, dolphins and whales that are around twelve million years old, but also the teeth of Ice Age mammoths.

There is also a contemporary witness, the geologist Heinrich Wolf. He reported in 1872: "The brickworks of Heiligenstadt and Nussdorf have long been known to geologists and paleontologists in Vienna as extensive sites for the remains of Elephas primigenius [=mammoth] and other fossil mammals. In 1863, the Imperial and Royal Court Minerals Cabinet received a whole elephant skull from Schegar's brickworks [...]. Three years ago Mr. Karrer acquired a lower jaw from the Kreindl brickworks for the university's geological museum and the museum of the Imperial and Royal Geological Institute has jaw remains with molars from 1857, precisely because of this."

The sand pits in the Türkenschanzpark mentioned above were also an El Dorado for fossils. The museum shops are full of - albeit poorly preserved - remains of plants that grew here 12.5 million years ago. The paleontologists Walter Berger and Franz Zabusch drew the following picture of life in 1952: "The plant remains of the Türkenschanze were apparently washed together in the mouth of a river whose banks were lined with dense, moist alluvial forest, while further inland light, dry savannahs and bush steppes - in some areas probably also free treeless steppes - expanded in other, probably more hilly and stony ones In places, however, there was maquis-like evergreen bush forest, occasionally with stands of pine trees. The landscape was partly reminiscent of the East African savannahs with gallery forests along the rivers, and partly also of Mediterranean dry hilly land.

The Glasau quarry in Ober St. Veit

When it comes to exploring the Glasau quarry, which is now completely overgrown, historical images and the rich collections in various museums help. The Austrian Image Archive of the Austrian National Library shows a hit in the search "Glasauer", a picture from 1930: It shows a steep wall with layers of rock thick a decimeter, which at best provided road gravel. The Natural History Museum has a very special piece from here: the ammonite Stephanoceras vindobonense. It occupies a period in the Jurassic (Metrozoic Age) that ranged from 175.6 to 161.2 million.

Alexander Lukeneder (Natural History Museum) showed that studying museum material makes sense. He examined around 4,000 fossils in various Vienna collections, cataloged and reinterpreted them. The long-vanished Glasau quarry also unexpectedly found fame here. (Thomas Hofmann, Mathias Harzhauser, June 24, 2021)