Bartolomeo Gastaldi (1818–1879) and the “glacial erratics” of the Torino Hill, NW Italy

In 1850, the Italian geologist Bartolomeo Gastaldi (1818–1879) first documented the glacial origin of the deposits belonging to the Rivoli–Avigliana and Ivrea end-moraine systems (Piemonte, NW Italy) in a joint note with Charles Frédéric Martins. The authors also interpreted as glacial erratics the large boulders, mainly made up of metamorphic rocks, scattered on the Torino Hill, thus envisaging an enormous advancement of Quaternary glaciers, well beyond the position of the two moraine amphitheaters. A decade later, Gastaldi corrected himself and recognised the boulders as derived from the erosion of Miocene marine conglomerates, invoking ice-rafting to explain their presence within marine sediments. This hypothesis was supported by no less an authority than Charles Lyell, who had visited the places in company of Gastaldi in 1857. Gastaldi’s ice-rafting hypothesis implied periods of large glacier development in Southern Europe during the Miocene, and soon entered the debate on the existence and extent of past glacial periods which animated the European geological community in the late nineteenth century.