erratic(redirected from erratic boulder)
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a piece of rock that differs in composition, shape, etc., from the rock surrounding it, having been transported from its place of origin, esp by glacial action
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
A rock fragment that has been transported a great distance, generally by glacier ice or floating ice, and differs from the bedrock on which it rests.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.