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Manitoba, Canada | A long time ago I read about how a small hard rock can become trapped by swirling currents on top of a softer rock and kind of spin and wobble around in place. Over time the hard rock wears a hole in the softer stone. Usually the stone can still be found at the bottom of the hole but maybe in your case either a top layer got chipped off or the stone was thin to start with for the hole to be right through it. | |
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