Very large rocks that have usually been broken off from cliffs or mountains and rolled to different places by ancient water or ice.
From Scandinavian 'bulla' or 'bull,' possibly related to 'boil' (to bubble or swell). The word came to English through Middle English, originally describing large water-worn rocks.
Boulders are evidence of ancient glaciers—enormous rocks deposited thousands of miles from their origin tell geologists exactly where ice ages reached, making these rocks into storytellers of Earth's climate history.
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