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In mid-1801, Gregory Watt, son of James Watt, the engineer, set off on European travels in hopes of recovering his health. During the winter of 1801–1802, Watt stayed in Paris and met the Scottish-American geologist William Maclure. Together they set off early in 1802 to travel through war-torn France and Italy, but in Italy they could only venture as far south as Naples, then in a state of anarchy. Here, despite Watt's consumption, they climbed, and descended into, Vesuvius and saw other evidence of recent volcanism. Watt thought this experience would change his mind about geological, especially volcanic, processes. As a result of the trip, he and Maclure saw a lot of European geology together. Watt was then inspired on his return home to make experiments on melting basalt and to study its cooling history and to attempt a “lithological” map of Italy from Calabria to Bologna and the eastern Italian Alps. The first work led Watt to “sit on the fence” over the then much-debated question of the origin of basalt. He believed it could have originated either from the action of heat or from water. Watt's early 1804 map was a brave attempt to delineate up to 46 separate lithologies on a “proto-geological” map of Italy. The lithologies are grouped by color, but do not refer to any stratigraphical classification. The map, therefore, is still at best a proto-geological map. Watt may well have met William Smith, the English pioneer of modern geological cartography, in Bath later in 1804, just before his death, but there is no further evidence. The criteria needed for such maps to be viewed as properly “modern” and “geological” are next considered. Gregory Watt died on 16 October 1804, aged 27 yr. A year before, he became the main critic on matters geological for the Edinburgh Review and there published up to nine reviews, mainly on mineralogy. He wrote but a single scientific article, of which he saw only preprints before his death. This article dealt with textural variation in basalt. Watt's legacy of publication is disproportionate to his significance to the history of geology and mineralogy.

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