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(1) Rock fragments more than 10, 25, or 50 cm in size, depending on the classification. Often, 1 m is taken as the upper limit for boulders (larger fragments being called blocks). Sometimes the term is applied only to spherical or rounded fragments.

Boulders are a major component of psephitic rocks (pebbles, shingle, and conglomerates); they occur frequently in alluvium and proluvium of mountainous countries and in glacial deposits. They are used under the name cobble (rubble) in the paving of roads and the production of crushed stone.

(2) Glacial boulders are rock fragments, irrespective of size, picked up and transported by glaciers; they are often rounded, polished, and covered with scratches (glacial striae). They occur in moraines and in glaciofluvial deposits. They are sometimes found in large quantities in areas of former glacial activity.

References in classic literature ?
Six trips he made in the five hours before Basuli reached the kopje, and at the end of that time he had transported forty-eight ingots to the edge of the great boulder, carrying upon each trip a load which might well have staggered two ordinary men, yet his giant frame showed no evidence of fatigue, as he helped to raise his ebon warriors to the hill top with the rope that had been brought for the purpose.
He had turned for that portion of the forest which abutted on the cliffs, and thus the mad race was taking the entire party farther and farther from the boulder where I lay concealed.
We withdrew behind an adjacent boulder to watch the actions of the little party, which stood huddled at the foot of another huge rock, their backs toward us.
Instead, she sat down on the boulder beside the girl.
46 deg; erratic boulders have, also, been noticed on the Rocky Mountains.
He was still three paces, however, from his victim's side when John upon the cliff above plucked up a huge boulder, and, poising it for an instant, dropped it with fatal aim upon the slinger beneath him.
He made a striding, clumsy leap on to another boulder, and stopped again, balancing himself, then said--
From behind my boulder I threw up the heavy express rifle--a mighty engine of destruction that might bring down a cave bear or a mammoth at a single shot--and let drive at the Sagoth's broad, hairy breast.
On the little plateau which crowned the barren hill there stood a single giant boulder, and against this boulder there lay a tall man, long-bearded and hard-featured, but of an excessive thinness.
Gilbert sat down beside her on the boulder and held out his Mayflowers.
And I sat down on the boulder the good man had just left, and opened the parcel to see the nature of my gifts.
In so doing he loosened a great boulder of rock, which fell upon George Curtis's right leg, crushing it frightfully.