The ‘gigantic boulders’ of the Torino Hill (NW Italy): geohistorical significance and geoheritage value

Large boulders, up to several metres in diameter and mainly made up of metamorphic rocks, are scattered throughout the Torino Hill in NW Italy. These boulders were originally included in Oligocene–Miocene conglomerate beds and were released by alteration of the host rock at the surface. In the past two centuries, their origin and mechanisms of emplacement in the conglomerate bodies were largely debated by both Italian and foreign geologists. Some of the boulders had been given proper names by the local people and had become the object of legends and rituals. Moreover, in the past, the boulders had an economic value, being used as construction stones or exploited to produce aggregates, lime and millstones. This, together with the progressive urbanization of the area, caused the disappearance of many of the large boulders once present on the Torino Hill. The remaining ones are presently not appreciated and are almost forgotten, even though they represent an invaluable geoheritage and deserve rediscovery and protection.