Scientist of the Day - Jean-Étienne Guettard
Jean-Étienne Guettard, a French geologist, mineralogist, and naturalist, was born Sep. 22, 1715. He was employed by the Duc d'Orleans as house naturalist and keeper of his cabinet, and when the duke died, he left Guettard a sum that allowed him to do pretty much what he wanted, which was traipse around France collecting plants and minerals, and observing the general lay of the land.
Guettard has several claims to geological fame, or at least respect. In 1746, he compiled and printed in the Memoires of the Paris Academy of Sciences the first geological map anywhere. In fact, he printed two of them, one showing all of Europe (fifth image), the second zeroing in on France and England (first image). He calls it a mineralogical map, which is more accurate geological map, since Guettard does not claim to show the rocks on the surface (like the subsequent geological maps of, say, William Smith), but simply shows where you are likely for find various metals, minerals, and types of stone. I am sure someone knows what the irregular circular band is that travels from France to England and back again, but it is hard to tell from the legend at upper right (third image). It is probably “pierre blanche,” or white limestone, such as is exposed at Dover in England.
In 1751, Guettard and a fellow traveler were visiting Clermont and the Auvergne region of France, part of what is called the Central Massif, where most of the mountains of France are located (see the detail of the bottom of his second mineralogical map, which shows Clermont and the Auvergne region, fourth image). Guettard wanted to see the Puy de Dôme, where Blaise Pascal's brother in law, Florin Perier, had carried a barometer, or Torricellian tube, up the mountain in 1648, which is why they were in the vicinity of Clermont (we wrote a post just three days ago on the Puy de Dôme experiment). Guettard observed quite a few mileposts, and some houses, built of a black stone that looked to him like volcanic rock. He was told it came from a village named Volvic, north of Clermont, and he sought it out, found the quarry, and traced the rock to cones in the mountains that looked just like old volcanoes.
Nearly every account I have read of Guettard’s visit to Volvic relates that Guettard, when he learned that the source of his mysterious building stone was Volvic, immediately exclaimed,: “Volvic, volcani vicus” – Volvic, volcanic village” – thereby explaining in one fell swoop that its name was Roman in origin and that the Roman's knew the area was once volcanic. Unfortunately, of the four accounts I read, not one cited a source for the story. This is nearly always an indication that the story has no historical foundation whatsoever, and I suspect that is true in this case. But I have passed the story on anyway, because it is now part of the Guettard legend.