About 320 million years ago, half of Yorkshire was the delta of a huge river that flowed south from Norway
and Scotland. The water deposited layers of granite sand which went on to form a hard sandstone, Millstone Grit. Erosion, mostly during the last stone cold Ice age between 80-10,000 years ago, has worn away the softer rock, leaving harder rock exposed, sometimes in improbable positions and other-worldly formations.