Belgium, the tropical swamp forest
PLANET BELGIUM
Part 3: A soggy bowl of plant debris
Go back 300 million years and our country is a swampy forest right on the equator. Amongst strange trees, cockroaches fly, giant dragonflies hover and gi-gan-tic millipedes crawl. In the foliage, the first reptiles lay their eggs. The plant-filled and soggy world of the late Carboniferous will be compressed into coal. This black gold has been mined and burned at a scorching rate since the 19th century. During the Carboniferous, the world collides into the gigacontinent of Pangea, with a mountain range stretching for 5,000 kilometres. In the process, Wallonia folds like an accordion against Flanders: the Ardennes rise up.
Reinout Verbeke
PLANET BELGIUM,
the odyssey of our country
Our patch of land in the heart of Europe has been on an eventful journey that has taken around five hundred million years. A long time before it actually existed as a country, Belgium started out near the South Pole, crossed the equator and has docked – for the time being at least – in the Northern Hemisphere.
It was a voyage full of dramatic collisions that have made our country a geological El Dorado. Let's hitch a ride with geologists, palaeontologists and citizen scientists as they reconstruct the landscape and the life that once swam, crawled or flew in it. Get ready to go on the most in-depth journey through our country, in five parts. This is part three.
There are hardly any signposts, so we get a little lost, but eventually we find the path to the Schmerling Caves, a cave complex on the border between the municipalities of Engis and Awirs, not far from Liège. Two climbers are preparing their ascent. This site is also known to archaeologists for the very first Neanderthal discovery ever made, by Philippe-Charles Schmerling in 1829, a quarter of a century ahead of the findings in the Neandertal near Düsseldorf. Had researchers realised much earlier that the skull belonged to a human species other than Homo sapiens, we might now refer to Engis man rather than Neanderthal.
But this human story was not why geologist Kris Piessens of the Institute of Natural Sciences brought me here. He puts his hand on the sloping grey-blue rock, which towers majestically above us: "full of crumbled limestone skeletons". It is a contemporary of the better-known limestone rocks in Dinant (the Rocher Bayard, the Rochers de Freÿr and the Citadel of Dinant) and the dolomite at Marche-les-Dames near Namur, where King Albert I died in a climbing accident. They bear witness to a calm tropical clear blue sea during the Lower Carboniferous (Dinantian, 359 to 330 million years ago).
Our country is located in the tropics a little too far south of the equator, and the Brabant Massif - the mountain range that lies beneath Flanders, so to speak - has already flattened out so much since Devonian days that material hardly flows to the ocean in Wallonia. So the seabed becomes a gathering place for lime: all those dead sponges, corals, brachiopods, crinoids, cephalopods, ... add lime to the bottom. And under the pressure of layers on top, this becomes limestone. Industry still mines them very actively, for example, for building materials, paper, food and toothpaste. Well-known stones from the Carboniferous are Belgian bluestone ('Petit Granit') and Meuse stone ('Pierre de Meuse'). The latter was already mined by the Romans to make milestones, funerary monuments, floor tiles and wall decorations.
The limestone rocks of the Schmerling Caves in Engis (near Liège) bear witness to a tropical ocean during the early Carboniferous. The limestone layers were deposited horizontally, but were shifted vertically in the massive collision of the supercontinent Gondwana. (Photo: Mathilde Antuna)
The limestone rocks of the Schmerling Caves in Engis (near Liège) bear witness to a tropical ocean during the early Carboniferous. The limestone layers were deposited horizontally, but were shifted vertically in the massive collision of the supercontinent Gondwana. (Photo: Mathilde Antuna)
360 million years ago. The supercontinent Gondwana (including Africa and South America) is on a collision course with our continent Laurasia (North America, Northern Europe, North-western Europe). But for now, we remain a clear blue tropical ocean, just as in the Devonian... (C.R. Scotese en GPlates)
360 million years ago. The supercontinent Gondwana (including Africa and South America) is on a collision course with our continent Laurasia (North America, Northern Europe, North-western Europe). But for now, we remain a clear blue tropical ocean, just as in the Devonian... (C.R. Scotese en GPlates)
What is immediately noticeable here in Engis as we look up is that the layered limestone banks, once deposited horizontally, are now in an entirely upright position. Huge geological forces must have hit here. "The Variscan mountain formation," says Kris, "caused by the collision of two large continents. We were on the southern edge of Laurasia (or Euramerica). That includes North America, Greenland, northern and north-western Europe plus part of Russia. But from the south, the supercontinent Gondwana is closing in. The continent from which we were torn off 480 million years ago (see episode 1 of Planet Belgium: "We are Avalonians"). Gondwana includes Africa and South America, so the collision will be a big one. And it leads up to that great clash we see here." Indeed, the limestone we can follow along a path on the right stops abruptly, turning into a black parcel of clay. "This is mud that was washed off the land back then."
Our clear blue tropical ocean becomes a muddy continental area during the Carboniferous period
Gondwana pushed up the area in front of it, just like a bulldozer. As a result, mountain ranges rose to the south of us: the Central Massif, the Eifel and finally the Ardennes, amongst others (see end of article). And the weight of those mountains pushed down the area beyond, our region in other words. So you get a long slope, along which huge amounts of sand, silt and clay flow into the foreland basin, call it the 'bowl' that Belgium has become. Marine life that depends on light and oxygen does not survive in that murky water. Our quiet, peaceful, blue sea of the early Carboniferous turns into a marsh delta, and the sea retreats.
"This is one of the important turning points in Belgium's geology," says Kris. "We are transformed from a clear ocean and marine system into a continental area where a huge amount of organic material accumulates. The aluminium-rich clay rock here in Engis sometimes contains so much organic material you could set it on fire. The layers were mined and burned between the 17th and 20th centuries to extract alum, which was then used, amongst other things, to clarify wine, cultivated here in the region.
330 million years ago. Gondwana collides with us. Our tropical ocean is transformed into a continent. We are a swampy 'bowl' into which lots of material flows from higher ground. And from time to time, we are inundated by the sea once more.
330 million years ago. Gondwana collides with us. Our tropical ocean is transformed into a continent. We are a swampy 'bowl' into which lots of material flows from higher ground. And from time to time, we are inundated by the sea once more.
Strange trees
In our swampy mangrove district of southern Belgium and the Limburg Campine region, the colour green predominates. The greening of our planet began slowly in the Silurian period (starting 443 million years ago) with the first land plants: mosses (with primitive rootlets, rhizoids) and the first mini-vascular plants (with an internal transport system) grew on the water's edge. They evolved long before that from green algae in the ocean. And their reproduction is with spores. In the Devonian period (from 419 million years ago), vascular plants grow larger and some start to resemble ferns. Ferns shoot up during the Devonian, forming the first groves. Just before the transition to the Carboniferous, the first tall trees appear, such as Archaeopteris, with real wood, leaves and sturdy roots.
But it is during the Carboniferous that the vegetation really goes wild. If you were to wade - with fishing boots - through our humid swamp forests of 310 million years ago, you would see tree ferns about ten metres tall, such as Psaronius. You would get a sore neck from staring at the scale tree Lepidodendron (up to 40 metres high) and at the seal tree Sigillaria (up to 30 metres). They are not real trees, but vascular plants in the lycophyte family. The spongy stem was a single 'pillar' that only 'forked' into two at the very top, when the plant was almost fully grown, forming a modest crown. The canopy back then was not as dense as in our current forests. Walking through a Carboniferous forest would be a rather strange experience for that reason alone.
The sturdy bark of these iconic plants shows a beautiful pattern of 'scars'. The marks were left by elongated leaves that systematically fell off during growth as the trunk grew thicker. In Sigillaria, the rows are vertical, in Lepidodendron the scars are like a spiral staircase heading towards the crown. They look so much like scales that fossil pieces of trunks have been mistaken for large reptiles.
These giant lycophytes owe their sturdiness to the bark, but above all to the root system. The main roots (actually root carriers) developed horizontally, with an enormous number of tiny roots sprouting from them. The thick roots grew around each other, intertwining with those next door to form shallow root plates. They clung to their neighbours, so to speak, making them more resistant to storms. Also iconic of the Carboniferous period are horsetail trees, such as Calamites, some 15 metres tall and resembling skinny Christmas trees as they grow, but with a bamboo-like trunk.
All the plants reviewed so far are spore plants that had to grow close to water to reproduce. Sperm and eggs find each other in that water. In Sigillaria and co., sausage-shaped 'cones' do hang at the top of the crown, but they are shedding spores, not seeds. The most important milestone for the flora in the Carboniferous is the evolution to seed plants, known as gymnosperms, meaning “unenclosed, naked seeds”. Naked refers to the fact there is no fruit around the seed, as in flower plants or angiosperms, which do not develop until much later, in the Cretaceous period..
Lepidodendron could grow to more than 40 metres tall. Its name, meaning scale tree, came from the diamond-shaped structures on the bark, which resemble a reptile's skin. They were left as 'scars' by elongated leaves, which fell off as they grew. The pattern progresses like a spiral staircase towards the crown.
Lepidodendron could grow to more than 40 metres tall. Its name, meaning scale tree, came from the diamond-shaped structures on the bark, which resemble a reptile's skin. They were left as 'scars' by elongated leaves, which fell off as they grew. The pattern progresses like a spiral staircase towards the crown.
Fossil spore cones (strobili) of Lepidodendron, known as Lepidostrobus. Plant parts (stem, roots, leaves, reproductive structures) are given separate species names because it is often not clear which pieces belong together. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Fossil spore cones (strobili) of Lepidodendron, known as Lepidostrobus. Plant parts (stem, roots, leaves, reproductive structures) are given separate species names because it is often not clear which pieces belong together. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
On Sigillaria the scars of fallen leaves run in straight lines across the bark. As if they were marked with a stamp or seal. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
On Sigillaria the scars of fallen leaves run in straight lines across the bark. As if they were marked with a stamp or seal. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
The bamboo-like stem and trunk of Calamites was hollow, which meant it became filled with sediment and preserved in 3D. At the knots, branches sprouted in wreath formation, with leaves arranged around the branches like spokes in a wheel. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
The bamboo-like stem and trunk of Calamites was hollow, which meant it became filled with sediment and preserved in 3D. At the knots, branches sprouted in wreath formation, with leaves arranged around the branches like spokes in a wheel. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
"The innovation in seed plants is that fertilisation no longer takes place in water, as with mosses and ferns," explains biologist and chief curator Elke Bellefroid of Meise Botanic Garden. "Wind blows the pollen grains into the female cone. This closes and a pollen tube grows from the grain to the egg, after which fertilisation takes place. An incredibly beautiful process, in my opinion. When the seed later falls out of the cone, it has everything it needs to grow into a new tree. For the first time, plants can leave the water's edge and colonise the dry and higher areas." The conifer-like Cordaites and Walchia are early gymnosperms at the end of the Carboniferous period.
Palmatopteris, a seed fern and presumably a climbing plant, among the stems of the conifer‑like Cordaites. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Palmatopteris, a seed fern and presumably a climbing plant, among the stems of the conifer‑like Cordaites. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Leaves of high-growing seed ferns. The leaves (with names like Pecopteris or Asterotheca) look similar to ferns but they are seed plants, not spore plants. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Leaves of high-growing seed ferns. The leaves (with names like Pecopteris or Asterotheca) look similar to ferns but they are seed plants, not spore plants. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Plants turn into black gold
The remains of ferns, giant horsetails and lycophytes, and coniferous trees piled up in the marshes of the 'bowl' that Belgium was then. And that plant material, especially from the coniferous species, provided our coal. You can still see nicely where those swamps once were if you follow the coalfields. It is a belt around the Brabant Massif (i.e. around Flanders): Borinage (near Mons), Centre (around La Louvière), Charleroi, Liège and the Campine. And looking beyond our own borders: in Ireland, Wales, central England, northern France to Dutch Limburg, the German Ruhr and Poland.
"Coal is the middle stage of a long process of carbonisation," says Xavier Devleeschouwer of the Institute of Natural Sciences. "In the marshes, where the water table remains high, conditions soon become deoxygenated. This stops bacteria from breaking things down and preserves the organic matter. You get parcels of peat in its dried form."
The next step is gradual coverage. The marshes become flooded and buried under younger sediments, causing an increase in temperature and pressure. "This changes the composition of the organic material, which consists of carbon, hydrogen and oxygen. The higher temperature and pressure expel the gases and water from the material, making it gradually purer in carbon."
"The second phase, after the peat, is that of brown coal or lignite," says Xavier. "In this, traces of plant remains are still visible, but the carbon content is already higher. After lignite you get to coal, charbon in French, or houille (northern French word, derived from the Germanic 'hulha' meaning ' hope' and in this case 'pile of raw material'). In coal, plant remains are rarely visible to the naked eye, and the carbon content is already 87 percent.
One metre of coal may have originally been a peat layer of more than twenty metres. Burial takes place at depths between one and five kilometres, causing temperatures to rise. At that depth, that coal can also produce natural gas, especially methane. And the miners knew it (read the insert at the end on mine gas). In the early 1980s, in the midst of an oil crisis, a drill went as deep as 5,648 metres in the village of Havelange, in the province of Namur, and was the deepest ever drilling in our country. The government hoped to find a large supply of natural gas, but their hope was in vain. "Our coal probably did once produce methane, however, it had escaped over all the millions of years."
As coal burial continues, and temperatures rise above 350 degrees Celsius, the metamorphosis begins. In the process, pressure and heat completely change the nature of the rock. "At this stage, graphite is formed: one hundred percent pure carbon. The carbon in your pencil."
The coal that exists on the planet today formed mainly during the late-carboniferous era. That coalification process did not repeat itself later to the same extent. Was it due to the unique geography of north-western Europe: wet tropics plus land that subsided exceptionally quickly, allowing organic material to accumulate? "Some give another reason," says Elke Bellefroid. "There were no fungi back then that could digest the harder plant material (lignin). Plants would have taken a lead in the evolutionary race with fungi during Carboniferous times. Organic material could thus sink undigested into the oxygen-poor swamps, later forming coal."
In two centuries, we have extracted, burned and pumped into the air the carbon that the swamp forests captured for millions of years and that the earth took millions more years to seal underground. The black gold that fuelled the industrial revolution and increased our prosperity has cost so many lives in the mines, as well as heating up and disrupting our climate. "That's certainly true," says geologist Michiel Dusar (Institute of Natural Sciences) and expert on the Carboniferous, "but without coal, wood would have remained the main source of energy until the 20th century, and there wouldn't be a single tree left standing in that case."
Age of insects
If the Devonian was the age of fish, the Carboniferous is the age of arthropods. Insects, centipedes and spiders. What crawled and flew through our impressive swamp forests? I visit palaeontologist Bernard Mottequin at the Institute of Natural Sciences. "Fossils are rare in themselves, but unlike plants, we have very few traces of terrestrial fauna. Even after two centuries of coal mining. The creatures may have been difficult to fossilise and, of course, a body of a tiny spider is harder to identify than a fern leaf.'
Bernard pulls a large book from the vintage cabinet of his desk in the Janlet wing, the building that has housed Bernissart Iguanodons since the early 20th century, and which also houses the three million specimen fossil collection. We turn the beige pages of Description de la faune continentale du terrain houiller de la Belgique. "This impressive 1930 work by French palaeontologist Pierre Pruvost is still the most complete overview of the fauna of the late Carboniferous period in Belgium."
I browse the collections, together with collection manager Julien Lalanne, searching for the fossils Pruvost had printed on fold-out pages. Using a lever, Julien slides open an ingenious cabinet system with hundreds of drawers. We put several on a table and open the plastic bags as if they were surprise eggs. The fossils are labelled with yellowing cards on which the Latin species names are often still written in decorative black letters. We see stunningly beautiful prints of cockroach wings. A relatively large number of these have been preserved, perhaps because their leathery armour fossilised well. And there, I see a wing print of an extinct insect - Palaeodictoptera says the name tag. It had six wings in total (four large, two tiny) and two long strings on the abdomen, which may have allowed more stable flight.
Most insects found in the Carboniferous strata had a life cycle in which the juvenile phase closely resembled adulthood. They grew through successive moults. Thus, in the Carboniferous, neither butterflies (with the caterpillar as a larva), nor flies (with a maggot as a larva), nor bees, ants or beetles had yet emerged. These days, insects undergoing major metamorphosis are in the majority.
The cockroach Miroblattites costalis, with the head, body, and wings well preserved. (Photo: Institute of Natural Sciences)
The cockroach Miroblattites costalis, with the head, body, and wings well preserved. (Photo: Institute of Natural Sciences)
I see petite but beautifully lined abdomens of primordial spiders (like Brachypyge), and to my delight, small sea scorpions (Eurypterus) and horseshoe crabs (Euproops), which had apparently adapted to brackish or fresh water. And then, I am handed pieces of Arthropleura, a millipede that could grow to more than 2 (!) metres long, the largest land invertebrate ever. An icon of the Carboniferous. The fossils of this herbivore that we have here in Belgium are little more than fragments of the armour on which, if you look closely, you can recognise a few nodules. But still: a rare trace that these amazing creatures once lived in our region.
Small horseshoe crabs, such as Euproops, also lived in the Belgian swamps of the late Carboniferous. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Small horseshoe crabs, such as Euproops, also lived in the Belgian swamps of the late Carboniferous. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
... and small sea scorpions like Eurypterus. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
... and small sea scorpions like Eurypterus. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Rows of protrusions on the dorsal skeleton of Arthropleura, the iconic millipede of the Carboniferous. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Rows of protrusions on the dorsal skeleton of Arthropleura, the iconic millipede of the Carboniferous. (Photo: Erik Van de gehuchte, Institute of Natural Sciences)
Artistic reconstruction of Arthropleura, which could grow to more than two metres in length. (Illustration: JW Schneider, TU Bergakademie Freiberg)
Artistic reconstruction of Arthropleura, which could grow to more than two metres in length. (Illustration: JW Schneider, TU Bergakademie Freiberg)
Another giant of the late Carboniferous and subsequent Permian period is Meganeura, which resembled a dragonfly in appearance. Some species were forty centimetres long and had a wingspan of seventy centimetres, the length of your arm. And they were formidable predators on other insects and small amphibians. No such fossils have been found in Belgium, due to the lack of proper strata, but they have been found in central France, in the Commentry coal mines. A cast in Evolution Gallery at the Institute of Natural Sciences is an insectophobe's worst nightmare.
Cast of Meganeura in the museum's Evolution Gallery. (Photo: Thierry Hubin, Institute of Natural Sciences)
Cast of Meganeura in the museum's Evolution Gallery. (Photo: Thierry Hubin, Institute of Natural Sciences)
Just imagine this swooping over your head: Meganeura, related to today's dragonflies, with wings spanning as wide as 70 centimetres. (Photo: Thierry Hubin, Institute of Natural Sciences)
Just imagine this swooping over your head: Meganeura, related to today's dragonflies, with wings spanning as wide as 70 centimetres. (Photo: Thierry Hubin, Institute of Natural Sciences)
Why were many insects able to grow to massive sizes in the Carboniferous period? The absence of predators will have played a role, and perhaps also the air. Michiel Dusar: "The increase of biomass on land caused a reverse greenhouse effect. CO2 levels in the atmosphere decreased, and oxygen levels increased. Up to 25% oxygen, more than the 20% we have now. All that oxygen allowed insects to grow larger. They don't have efficient lungs and thus had to rely on higher concentrations in the air."
That higher oxygen level made the forests, especially the higher elevation conifer forests, more susceptible to wildfires - with lightning as a match. "The frequent forest fires eventually caused oxygen levels to stabilise at 20%."
Eggs on dry land
During the Carboniferous, there is other life besides gymnosperms that begins to move away from the water. They are the first amniotes, ancestors of reptiles, birds and mammals. Some amphibians - evolving from lobe-finned fish in the Devonian - had adapted. Not only could their bones and muscles support their body, their embryos developed in a membranous sac filled with amniotic fluid. Thanks to that protective membrane, offspring no longer needed to be born in water. The eggs were dropped on the new terrain: the moist litter of tropical forests.
Hylonomus, one of the earliest reptiles. (Reconstruction: Nobu Tamura)
Hylonomus, one of the earliest reptiles. (Reconstruction: Nobu Tamura)
Then, what emerged from those eggs were not swimming larvae, but immediately miniature salamanders, which no longer needed to undergo metamorphosis. And in the fight against dehydration, eggs gained a shell. By definition, these amphibians had thus become reptiles. An adaptation that will give access to new territory, up to the driest areas, including in the Permian, the period following the Carboniferous, and the last of the so-called Paleozoic. And it will enable the further evolution of reptiles, birds and also mammals. Of those first amniotes, except for a few disputable paw prints, no fossils have been found in Belgium for now.
New in the Carboniferous: plants and tetrapods move away from the water
"Historical collections are so important," Bernard says as he shows me another magnificent fossil of a 315-million-year-old cockroach. "Carboniferous fossils were collected by miners and engineers in the 19th and 20th centuries. We should be grateful to them, because all the coal mines have since been flooded. Fossils were an important guide for mine management, especially those in the marine sediments below and above the coal seams. They allowed them to link up the coal layers, as these were often folded and interrupted by the intense tectonic activity at the end of the Carboniferous and beyond."
Belgium and its accordion
Tectonics! We could almost forget that the supercontinent Gondwana is colliding with our continent Laurasia in slow motion. Such land masses are many tens of kilometres thick. "Don't think of it as cars colliding,' says Kris Piessens, "but as large lumps of cheese being pushed against each other. Closer to the surface, rock will fracture and rearrange itself; deeper down, the layers fold or are flattened. But across all depths, a large fracture can form, along which thick slabs of rock are pushed over others and thus piled on top of each other. This is a thrust fault. All these horizontal processes lead to vertical thickening: the part that goes up into the sky we know as mountains, but an even larger part is pushed into the earth, forming the roots of the mountain range."
And the scale on which this happens must have been gigantic. "If you already find the Himalayas - the result of India colliding with Eurasia - impressive, just think what happens when two gigantic continents collide." At the end of the Carboniferous, some 300 million years ago, Variscan mountain formation is at its peak. It is a mountain range some 5,000 kilometres long. Remnants in the west are the Appalachian Mountains, in the east the Ural Mountains, and centrally, in Europe, the Central Massif, the Armorican Massif, the Vosges Mountains, the Black Forest, the Bohemian Massif, Sardinia, Corsica, the Harz Mountains, the Eifel, and virtually the entire Iberian Peninsula, amongst others.
And what about here? "Our country is often on the edge in geological history, vulnerable to tears and collisions. And during the Carboniferous we are on the southern edge of Laurasia, exactly where Gondwana is heading. We are right on the collision course."
300 million years ago. The second major mountain formation takes place. The Variscan mountain chain stretches from the Appalachian Mountains, across European mountain ranges, such as the Central Massif, the Vosges and the Ardennes, as far as the Urals.
300 million years ago. The second major mountain formation takes place. The Variscan mountain chain stretches from the Appalachian Mountains, across European mountain ranges, such as the Central Massif, the Vosges and the Ardennes, as far as the Urals.
Positioned on the northern edge of Gondwana, on the 'bumper', are France and southern Germany (in case you were wondering: Northern France and Northern Germany were on our continent from when we were Avalonia 480 million years ago). The collision causes havoc. "The remains of our oldest mountains - still from the Caledonian mountain formation - are torn from their roots and incorporated into the new, higher mountains that the Ardennes are now becoming. The limestone layers break and are sometimes literally turned upside down: the youngest layers at the bottom, the oldest at the top. And the coal basins fold."
Why Flanders is flat and Wallonia all askew. The Brabant Massif - the mountain range that sits beneath Flanders - remained rock solid during the peak of Variscan mountain formation (starting 305 million years ago). It protected Flanders from major folds and gave Wallonia an accordion-like relief. The line happens to lie on the language border: the Midi fault. (Figure: Léon Dejonghe)
Why Flanders is flat and Wallonia all askew. The Brabant Massif - the mountain range that sits beneath Flanders - remained rock solid during the peak of Variscan mountain formation (starting 305 million years ago). It protected Flanders from major folds and gave Wallonia an accordion-like relief. The line happens to lie on the language border: the Midi fault. (Figure: Léon Dejonghe)
And then the deformation hits an unyielding wall in Belgium: the Brabant Massif. More or less along our language border, this causes an elongated thrust fault: the Faille du Midi, the Midi fault. The southern terrain folds up like an accordion against the Brabant Massif. You can feel its waves when you drive through the Condroz, between Namur and Dinant: seven rows of hills.
The Brabant Massif, which acted as a shock absorber, is the reason why flat Flanders is so different from warped Wallonia.
The second great mountain formation came to a dead end at the present language border: Wallonia folded like an accordion, Flanders remained flat
This was also noticeable in the coal mines: in Limburg, the coal layers are gently sloping, while the Walloon mining engineers often cursed, because there they are folded.
The Variscan mountain formation is a global event: it brings the whole world together to form Pangea. And that will change the playing field: larger continents undivided by oceans tend to become drier. Gymnosperms and reptiles have already developed some good weapons and are ready. It will do them no harm.
André Dumont found coal in Limburg
André Dumont, professor of mining engineering at KU Leuven, proclaimed for 20 years that there was coal in the Campine region of Limburg. His hypothesis was based on an 1876 report by his former professor Guillaume Lambert. Here, he argued that a northern coal basin extended from German Westphalia to England, with its heart in Belgian Limburg.
The hypothesis faced scepticism, but Dumont persisted. And this inspired his students: in 1896, one of them founded a company that raised 180,000 francs for an exploratory well at Elen. Drilling began in late 1898, but after nearly two years, the team encountered 'red rocks' at a depth of 800 metres. The coal was much deeper but the money had run out.
A new company was formed in May 1901. The group began drilling in the municipality of As. On 2 August, in Spa, while Dumont and his wife were on a wellness retreat, a telegram arrived: coal had been found at a depth of 541 metres. "I knew it," was his laconic response. On the train to As, he couldn't keep his mouth shut, and the news leaked out immediately.
What followed was a veritable coal rush. Coal was found in an area of 50 by 8 kilometres, and seven companies were granted mining permits: in Beringen, Waterschei, Winterslag, Zwartberg, Houthalen, Zolder and Eisden. Dumont became manager of the mine that bore his name, in Waterschei. But he would not live to see the opening. Because of World War I, it did not begin until 1924, four years after his death. Limburg's first mine, known as Winterslag (where C-Mine is today), was operational as early as 1917.
Silent and not so silent killers
Miners had two deadly enemies. One struck in a flash, the other took years to destroy you from the inside.
Le coup de grisou was the most feared. Grisou is a colourless and odourless mine gas, a mixture of methane, trapped in the coal seams, and oxygen. Once the concentration exceeds five percent and someone ignites a flame, an explosion ensues. In Belgium alone, there were more than 360 recorded casualties from this gas.
To detect the invisible danger, miners took canaries into the depths. The birds are first to sense a rising gas concentration and become agitated. Nervous canary? Get out now! Later, there were special miners' lamps whose flame colour betrayed the presence and amount of mine gas. And even later, devices measured the amount of the gas mixture directly.
But before measuring devices, lamps and canaries, a more sinister method existed. A worker, wrapped in a wet blanket or monk's habit, crept through the corridors with a burning torch above his head. If grisou had accumulated on the ceiling, it ignited or exploded - with the man underneath. They did it to earn a bonus. The story goes that prisoners were also used, in exchange for a shorter sentence.
Those who escaped a coup de grisou did not escape the dust. Anthracosis is coal dust in the lungs, silicosis is fine quartz dust from the surrounding rock. The latter was worse, because lung tissue damage continued long after the miner had quit working underground. Lung capacity declined year after year, like a belt being tightened one hole at a time. Anthracosis and silicosis killed many thousands of miners.
Photo: former miner Wilfried Dekinder shows his miner’s lamp, in which the size of the flame indicated the amount of mine gas. (Photo: Reinout Verbeke, Institute of Natural Sciences)
The Institute of Natural Sciences is reconstructing the wanderings of the patch of land we know today as Belgium: from the South Pole to the place where we're located today. A series on our country's unique geology in five longreads, five podcast episodes (in Dutch) and five posters.
Every two months in 2026 a new episode will appear on
www.naturalsciences.be/r/planetbelgium
With support from the Wernaers Fund of FNRS.
A heartfelt thanks to, among others:
- Geologist Kris Piessens (Institute of Natural Sciences) for inspiration and guidance
- Geologists Michiel Dusar and Bernard Mottequin (Institute of Natural Sciences) and biologist Koen Martens (Institute of Natural Sciences) for reviewing
- Sound designer Joris Van Damme and musician Bart Couvreur for the podcast
- Illustrator Vinciane Decamps (Vinch Atelier) for the posters
- Videomaker Stijn Pardon (Institute of Natural Sciences) for the trailer
- Erik Van de gehuchte (Institute of Natural Sciences) for the focus stacking of fossil plants and animals from the Carboniferous.
- Oneliner Translations for this text in English
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