In geology , a boulder (or rarely bowlder ) is a rock fragment with size greater than 25.6 cm (10.1 in) in diameter. Smaller pieces are called cobbles and pebbles . While a boulder may be small enough to move or roll manually, others are extremely massive. In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones.
2-424: The word boulder derives from boulder stone , from Middle English bulderston or Swedish bullersten . In places covered by ice sheets during ice ages , such as Scandinavia , northern North America , and Siberia , glacial erratics are common. Erratics are boulders picked up by ice sheets during their advance, and deposited when they melt. These boulders are called "erratic" because they typically are of
4-769: A different rock type than the bedrock on which they are deposited. One such boulder is used as the pedestal of the Bronze Horseman in Saint Petersburg , Russia. Some noted rock formations involve giant boulders exposed by erosion , such as the Devil's Marbles in Australia 's Northern Territory , the Horeke basalts in New Zealand , where an entire valley contains only boulders, and The Baths on
#109890