Jean Francois Aubuisson de Voisins (1769-1841) was a French geologist and engineer who studied under Abraham Gottlob Werner at Freiberg together with Humboldt, von Buch and Jameson. Werner had coined the term geognosy to define a science based on the recognition of the order, position and relation of the layers forming the earth. His theory of the marine origins of the Earth’s crust (Neptunism) was widely accepted at the time. Aubuisson however showed that igneous rocks such as basalt were similar to surface lava flows, and were not chemical precipitates of the ocean. His two-volume Traite de Geognosie, published in 1819, was one of the earliest geology books in French. It was highly successful, and gained him wide professional recognition. Volume 2 describes different categories of rocks and minerals, and formations including basalt dykes, ore deposits, and intruded veins. It also puts forward arguments challenging some of Werner’s theories.