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In geology, a boulder is a rock fragment with size greater than 25.6 centimetres (10.1 in) in diameter.[1] Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive.[2] In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones. The word boulder is short for boulder stone, from Middle English
Middle English
bulderston or Swedish bullersten.[3] 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.[2] They are called "erratic" because they typically are of a different rock type than the bedrock on which they are deposited. One of them 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
Horeke basalts
in New Zealand, where an entire valley contains only boulders, and The Baths
The Baths
on the island of Virgin Gorda
Virgin Gorda
in the British Virgin Islands. Boulder
Boulder
sized clasts are found in some sedimentary rocks, such as coarse conglomerate and boulder clay. The climbing of large boulders is called bouldering. See also[edit]

Road debris Monolith

References[edit]

^ Wentworth C.K. (1922). "A scale of grade and class terms for clastic sediments". Journal of Geology. 30 (5): 377–392. Bibcode:1922JG.....30..377W. doi:10.1086/622910. JSTOR 30063207.  ^ a b "Boulder". Dictionary.com. Retrieved 24 August 2013.  ^ boulder. (n.d.) Online Etymology Dictionary. Retrieved December 9, 2011, from Dictionary.com website.

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