Millstone grit

Millstone Grit is the name given to any of a number of coarse-grained sandstones of Carboniferous age which occur in the British Isles. 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.

The term gritstone (usually capitalised by British rock climbers) describes any sandstone composed of coarse angular grains, and specifically refers to such sandstones within the Peak District, Pennines and neighbouring areas of Northern England.

Rocks assigned to the Millstone Grit Group occur over a wide area of Northern England, where they are a hugely important landscape-forming element of the rock succession. They also occur in parts of northeast Wales and northwest Ireland. The group comprises a succession of sandstones, mudstones and siltstones, the specifics of the sequence varying from one area to another. They give rise both to a number of escarpments, known locally as edges, and a series of high plateaux throughout the region, many of which are of considerable cultural significance.

They are the major landscape-forming rocks of the northern part of the Peak District (the Dark Peak) and of its eastern and western flanks in the counties of Derbyshire, Staffordshire and Cheshire. The great expanses of moorland around Bleaklow and Black Hill and fringed with broken outcrops of gritstone are characteristic of the area.

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