What are
Boulders ?
·
In geology, a boulder is a rock with grain
size of usually no less than 300 millimetres (12 in) diameter.
·
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.
·
In places
covered by ice sheets during Ice Ages, such as Scandinavia,
northern North America, and Russia, glacial erratics are
common.
·
Erratics
are boulders picked up by the ice sheet during its advance, and deposited
during its retreat.
·
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 in New Zealand, where an entire valley contains
only boulders, and The Baths on the island of Virgin Gorda in
the British Virgin Islands.
