Millstone Grit is the name given to any of a number of coarse-grained
sandstones of
Carboniferous age which occur in
Northern England. The name derives from its use in earlier times as a source of
millstones for use principally in
watermills. Geologists refer to the whole suite of rocks that encompass the individual
limestone beds and the intervening
mudstones as the Millstone Grit
Group. The term Millstone Grit
Series was formerly used to refer to the rocks now included within the Millstone Grit Group together with the underlying Edale Shale Group.