Desmarest, Nicolas (1725–1815)

French naturalist. He became a champion of volcanist geology, countering the widely held belief that all rocks were sedimentary. He wrote extensively for the Encyclopédie. Studying the large basalt deposits of central France, Desmarest traced their origin to ancient volcanic activity in the Auvergne region. In 1768 he produced a detailed study of the geology and eruptive history of the volcanoes responsible. However, he did not believe that all rocks had igenous origin, and emphasized the critical role of water in the shaping of the Earth's history.

Desmarest, born near Troyes, moved to Paris and occupied minor government offices. Gradually he staked out for himself a scientific career, publishing charts of the English Channel and making geological tours.