About a million years ago, the world's temperature dropped and the polar ice caps thickened. Millions of tons of ice built up on the original ice pack, and the weight of this build-up pushed the edges of the ice pack outward, towards the equator.
An enormous blanket of ice moved slowly southward over what is now New England, plowing up the soil and absorbing rock and dirt into itself by a slow-motion churning.
Huge boulders (known as glacial eccentrics) were picked up and carried by the advancing ice and dropped helter skelter as three or four glaciers advanced and retreated.
When that last glacier (the Laurentide Glacier) came and went between 10,000 and 20,000 years ago, it left a pile of boulders in what is now our yard, more specifically, our garage.
Most we've been able to move.
This one will require a little more persuasion.
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