Smooth polished rocks on the shore at Thornwick Bay, looking towards the golden cliffs of Flamborough, Yorkshire, England, United Kingdom, Europe

Animal forms in the 9000 year old ground and polished Stone Age rock art at Leiknes, Norway, Scandinavia, Europe

Animal forms in the 9000 year old ground and polished Stone Age rock art at Leiknes, Norway, Scandinavia, Europe

Polished rock left on the side of the valley by the retreating Mer Du Glace, Chamonix, Haute Savoie, France, Europe

Stones and rocks polished smooth by the sea at Famara Beach, Lanzarote, Canary Islands, Spain, Europe

View of rock formation called Hollow Rock at sunset, Lake Superior, Grand Portage, Minnesota, USA

View of rock formation called Hollow Rock at sunset, Lake Superior, Grand Portage, Minnesota, USA

Polished smooth stones and pebbles on the sea shore, in Olympic national park. Varied shapes and sizes, Olympic national forest, Washington, USA