Glacial erratic

A glacial erratic is glacially-deposited rock differing from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare (to wander), and are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock (16,500 tonnes or 18,200 short tons) in Alberta.

• http://en.wikipedia.org/wiki/Glacial erratic