Gritstone

British gritstone was used for millstones to mill flour, to grind wood into pulp for paper and for grindstones to sharpen blades.

[1] "Millstone Grit" is an informal term for a succession of gritstones which are to be found in the Pennines (including the Peak District) of northern England.

[2] These sediments were laid down in the late (upper) Paleozoic era, in the Carboniferous period, in deltaic conditions.

The Millstone Grit Group is a formal stratigraphic term for this sequence of rocks.

[3] The rough surface provides outstanding friction, enabling climbers to stand on or grip the subtlest of features in the rock.