Volcanic by John Brewer

Author:John Brewer
Language: eng
Format: epub
ISBN: 9780300274431
Publisher: Yale University Press

Fire and water

Where then did volcanoes and Vesuvius fit into this story? To understand this we need to see how the relative importance of volcanoes in the study of the earth shifted in the late eighteenth and early nineteenth centuries. Werner’s extremely influential classification of rocks treated volcanic materials as unimportant and superficial. Water, not fire, was considered as the crucial agent in rock formation, whether in the form of a biblical flood, a receding ocean or marine inundation of the land. Volcanoes were not considered important in the formation of mountains; on the contrary, mountains made volcanoes. But from the 1750s, the field work of a number of French naturalists in the regions of the Auvergne, Vivarais and Velay in the Massif Central revealed the presence of numerous extinct volcanoes; soon others were discovered in northern Italy, Germany and Portugal. Volcanic action was baked into the history of the earth. Nicolas Desmarest, a French government official who had travelled in the Auvergne, argued that columnar basalt, found both in the Auvergne and in spectacular form in the Giant’s Causeway on the north coast of Ireland, was composed of volcanic rocks, because such prismatic forms could be found emanating from the extinct cones of the volcanoes in the Auvergne. The potential implications of such views, which came to be shared by other savants in France, Italy and Germany, were far-reaching: they implied a much greater role for heat in the development of the earth, and that volcanoes were not superficial, recent phenomena but had a much longer history. Desmarest’s views were reinforced by his observation of both extinct and active volcanoes in Italy (the only live volcano he ever saw was Vesuvius), but they remained controversial, triggering an intense debate about the nature and role of basalt. When, in 1788, the members of the recently founded Naturforschenden Privatgesellschaft (Natural History Society) in Berne set the essay prize question, ‘What is basalt? Is it volcanic, or is it not?’, they knew they were posing one of the most controversial questions of the day.31

The responses to this question were complex, but generally fell into one of three positions. The first argued that basalt was not volcanic but rather an aqueous precipitate formed as the global ocean receded. This was the so-called ‘Neptunist’ view taken by Werner and many of his followers. The second maintained that basalt was an igneous rock but was produced by the solidification of subterraneous, not volcanic, lava. The third position argued that basalt was indeed an igneous rock produced by volcanoes. (Both of these last two views, despite their difference, were characterised as ‘Plutonist’.) Charles Daubeny, the author of A Description of Active and Extinct Volcanos (1826), represented these different positions by placing them on what he called ‘The Geological Thermometer’, an image scaled from 1 to 100 that showed ‘the opinions attributed to various geologists with respect to the origin of rocks’. At the highest temperature were the Plutonists, then shading towards the middle were the Vulcanists, while at the bottom were the Neptunists.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.