Clinchers of the basalt controversy; empirical and experimental evidence

The 18th century basalt controversy had two aspects: its sedimentary versus volcanic nature, and its superficially combustive versus deeply derived origin. The neptunistic answer to the first question prevailed around the middle of the century owing to the general validity of the Wernerian lithostratigraphy at that time. Clinching evidence for the volcanic nature of basalt came forward in the final quarter of the century, essentially from countries with active or recently extinguished volcanoes-like Italy and France-while fusion experiments and chemical bulk analyses proved the similarity of basalt and basic lavas. Throughout the 18th century, the origin of basalt was held to be due to the superficial combustion of coal, bitumen, oil, sulphur, etc., even by confirmed Vulcanists. At the very end of the century Werner's lithostratigraphic system became liable to serious doubts. Basaltic volcanoes were found to have derived their material from underneath Werner's oldest formation: the granitoid 'Urgebirge', where neither combustible matter nor air could have been available. Also the melting temperatures of lava and basalt were experimentally shown to be higher than the temperatures of burning combustible materials. Thus a firm link was established between the hypotheses of Vulcanism and Huttonian Plutonism.