It's generally known that Long Island was formed by the action of glaciers about 20,000 years or so ago. But the beginning of the story goes back way further than that. The foundation of what was to become mainland Long Island used to be the Appalachians, which once stood three miles high and reached from far inland to the shore of the Atlantic Ocean. The Appalachians themselves had been plowed up by the earth's shifting crust when the water that had covered most of North America for millions of years finally receded back at the end of the Paleozoic era. Over the next couple of million years, the mountains were ground down by the elements and basically washed into the ocean, where the sediment built up to form Long Island's basement.

More shifting brought that foundation close to the surface so that when the glaciers finally started moving down from the north, sheets of ice, a couple of miles high themselves, ran smack into it. Operating like giant snowplows, the glaciers pushed things southward and left them lying around in piles, then backed up again, leaving the North shore with cliffs and New England-y looking hills and dales, in much the same way that the gravel from your driveway winds up out in the road. If this had happened 20,000 years later, the glaciers, just like the snowplows of today, would have proceeded to bury your car and then back up into the side of the house.

The landscapes left behind by glacial action are called moraines and there are a couple of different kinds. According to Les Sirkin, in his 1995 book, entitled “Eastern Long Island Geology with Field Trips,” two ice advances were responsible for creating the moraines. “The southernmost line of hills runs from Bay Ridge in Brooklyn through central Long Island, then into the South Fork, where it enters the Atlantic Ocean a few miles west of Montauk Point. This is a ‘terminal moraine' that formed along the edges of both ice sheets at the time of their maximum extent.

“North of the terminal moraine are additional lines of hills that formed as the glacier temporarily stabilized its position during its retreat. The hills along the north shore of Long Island are examples of these ‘recessional moraines' as are the elevated parts of Shelter Island and the headlands along the north side of the South Fork.” So the Heights are a recessional moraine. As warming temperatures forced the glaciers to retreat back north, they then dropped a lot of what they'd carried south with them, including those rocks at Quinipet.

Somewhere along the line, the basin that would become Long Island Sound got scoured out and filled up with water — fresh water at first. The sound, which is 110 miles long, 21 miles wide and approximately 65 feet deep, was a fresh water glacial lake for several thousand years. Sediment, hundreds of feet thick, accumulated in this lake. Eventually a breakthrough in the east caused the lake to drain. Sea level, which was 350 feet lower 20,000 years ago, began to rise again from the melting glaciers, the abandoned lake filled with saltwater and not much of any great interest has happened since then.

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