The best type of stone from which to manufacture quern-stones are igneous rocks such as basalt. These have naturally rough surfaces, but grains do not detach easily, so the material being ground does not become gritty. However, such rocks are not always available, meaning that quern-stones have been manufactured from a wide variety of rocks, including sandstone, quartzite and limestone. Quernmore Crag near Lancaster in England is named after the quarrying of millstone grit used to make quern stones in these parts. The names of the mountains of Whernside and Great Whernside in the Yorkshire Dales have the same origin.