. As gritstone is a fluvial sedimentary rock, it frequently shows signs of cross-bedding or current bedding. It is quarried for building material. British gritstone was used for millstones to mill flour, and grind wood into pulp for paper, and for grindstones to sharpen blades. The Millstone grit is a stratigraphic gritstone unit exposed in the Peak District of north central England. It was laid down in the late (upper) Paleozoic era, in the Carboniferous period, in deltaic conditions. Rock cl… (More on Gritstone)