The Scientist of The Day!

Nicolas Desmarest, a French geologist and cartographer, was born Sep. 16, 1725. When Desmarest began his work, it was thought that basalt formations, such as the Giant’s Causeway in Ireland, were some sort of sedimentary deposits. In 1763, Desmarest began mapping the Auvergne region of central France, which contains most of that country’s mountains. He noticed that the mountains were not at all like the Alps, but had the shapes and features of volcanoes, even though no active eruptions had ever been recorded in France. And he found basalt formations everywhere, the source of which he was able to trace to the volcano-like craters.

In 1771, Desmarest presented a geological map of the Auvergne region to the Paris Academy of Sciences, locating all the craters and basalt formations, and in the accompanying memoir, he argued that the mountains of the region were once volcanic, and that basalt is a volcanic, or igneous, rock. Desmarest was really the first to suggest that volcanoes had been important forces in shaping the face of the earth in the deep past, and that wherever we see basalt, we are observing the remains of past volcanic action. Here is a link to Desmarest’s map from the 2004 exhibition, Vulcan’s Force and Fingal’s Cave; the online version shows a detail of the map. The complete map is shown above, as well as two other details. The last one shows the map legend, and indicates that Desmarest understood fully that one can distinguish ancient lava flows from more recent ones, and that the “prismes de basalt” (columnar basalts) were clearly related to the lava flows.