The structure and history of the earth. However, as a science, it has a history of its own and geological events. So in this blog, I do not just want to talk about how we learned about the Earth, but also how geology made history (who wants to can listen to a podcast and learn more about me and my blogging).
In 1751, the doctor visited French Auvergne, known today for its conical mountains, as well as Puys, and the myth of a terrible man-eating beast. 250 years after Guettard. Guettard could not have guessed at that time but somehow both things hang together and as a geologist I was on the way to the land of the beast nearly 250 years after Guettard.
In his youth, Guettard had helped his grandfather, a pharmacist, to find medicinal herbs. He had observed that certain plants only occur on soils with a certain composition, an observation that aroused his interest in geology. Later, he served as a naturalist the Count of thus took him to this wild area.
The Auvergne and surrounding provinces are characterized by lonely marshes and swamps, from which rise conical hills and steep cliffs with strange, columnar rock formations. Some of these strange hexagonal pillars are becoming fossilized bamboo forests or huge crystal formations. The regular columns were simply called by the locals, roof tile bricks, as they were mined to cover roofs or build walls.
In the summer of 1764 appeared in the Gevaudan, which then included the southernmost portion of the Auvergne and parts of the present-day Lozere, suddenly a man-eating beast. There are numerous contemporary representations of the beast, mostly very imaginative. The landscape played an important role in the myth that emerged around the beast of Gevaudan.
The first victim was a 14-year-old girl who was attacked and torn up near the village. One month later, another girl was killed. The authorities warned the population of the beast, which was described as a cross between a hyena and a wolf, but as big as a donkey, with a terribly open mouth. Panic quickly spreads the French king what he wants to send his best hunters to the area. Who specializes in wolf hunting, said: This beast will not be easy to kill. In fact, over 5,000 square kilometers of marshy terrain made huntings almost impossible. The beast also hid from its captors in the narrow wooded gorges carved into the hard rock.
But back to Guettard, who survived his journey unscathed and should turn the geology of that time completely upside down. His attention was attracted to Vichy by one of those strange tile tiles. He recognized in the dark rock a surprising resemblance to a rock sample of Etna, which he had seen in the Natural History Cabinet of the Count of Orleans. Guettard quickly asked for the place of origin of the rock. He traveled there and recognized the quarry as an old fossil basalt lava flow. Whats more, he could trace the river back to a Puy. The Puy was actually a volcano that had been built during a volcanic eruption of ash and slag. One recognizes the layers which are deposited during individual volcanic eruptions so in this cross section by a volcanic cone at Narse.
Guettard finally recognizes the entire territory of Gevaudan as an ancient volcanic landscape. The lava flows are mostly made of dark basalt, very weather resistant this rock forms steep cliffs and deep gorges. The dense rock in the underground, along with basalt, older metamorphic shale, forms a water-impermeable layer. The dammed up water leads to the formation of swamps and bogs. Silent, forest-surrounded Maar lakes. Old blight. Old volcanoes, on the other hand, form the characteristic conical puies, which have a crater at their top. The alleged bamboo fossils were basalt columns that are formed when the lava cools and shrinkage cracks break the rock into regular hexagons. From this, the roof tiles are obtained, as in this quarry near the village of Le Pont de Alleray.
In 1752 Guettard published his observations and around 1771 another amateur researcher, Nicholas Desmarest, made a detailed map of all the volcanoes and lava flows of the Auvergne. The scholar surprised this card with two important findings. First, volcanic phenomena were much more widespread than previously thought. Since the active volcanoes in southern Italy have been known in Europe at that time, it has been assumed that the volcanic forces only play a minor role in shaping the earth’s surface. But now you could see all the mountains and landscapes could be shaped by volcanoes. The thickness of the deposit also