Spinkwell is a resistant grey variety of sandstone consisting predominantly of quartz grains but with some mica grains providing a hint of sparkle. Dating from the Upper Carboniferous age about 340 million years ago, it is part of the sequence of rocks making up the coal measures and was formed during a period of submergence within a tropical coastal environment. Spinkwell sandstone and local variants form the material for most of Bradford’s buildings. On the city’s boundary lies the huge Bolton Woods quarry which still supplies stone locally but also far and wide, whereas Spinkwell Quarry was located close the to the city centre and has not been operational for a century or more. The lithograph dating from 1870 gives some idea of its appearance and the working conditions of the time. Today, Spinkwell Quarry has been colonised by large retail sheds and factories and a large area has been converted into the Boar Well urban nature reserve, a name referring to a medieval legend about a particularly savage local wild boar. There is, however, no mention of the enormous quarry which once existed here, although traces remain, including walls, scree and some quarry face, and the name persists in the renovated Spink Well.