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Glacial Reminders All Around Us

By Dan Fagin | Staff Writer

We don't have dinosaur bones like the Dakotas or outcroppings of ancient bedrock like New England, but Long Island has its own array of geologic treasures, and most are easily accessible to the public.

As a place where the most recent glacier ended its 1,000-mile journey south from Canada just 22,000 years ago, Long Island's landscape is laden with signs of the vast size and power of the great ice sheets.

Rockhounds have been coming to Montauk Point for more than a century to view the layered cliffs and the boulders on the beach. The narrow striations near the top of the cliffs date from a time about 19,000 years ago when the area was an icy lake fed by the waters of the retreating glacier, while the lower and darker cliff layers may have been deposited by an earlier ice sheet visiting Long Island.

The boulders at Montauk, like virtually all the loose rock on the surface of Long Island, are ``erratics'' that were broken off New England bedrock and carried south by the ice sheet. Smithtown's Target Rock is an erratic, and so is Shelter Rock in Manhasset, which may be the largest boulder in New York State.

Caumsett State Park in Smithtown, the Amagansett National Wildlife Refuge and Garvies Point Preserve in Glen Cove are excellent places to view erratics and striated cliffs. At Garvies Point, the lower cliff layers were deposited tens of millions of years ago, before glaciers came to Long Island. The offshore boulders at Amagansett show where the glacial moraine, or elevated ridge, that runs from Brooklyn to the East End finally leaves the Island and continues offshore. That terminal moraine marks the southernmost extent of the last glacier.

Suffolk County's unique pine forests, which survive in arid, sandy soil deposited by the last glacier, are on display in parks such as Cranberry Bog County Park in Riverhead and Robert Cushman Murphy County Park in Manorville. Both parks also feature ponds that formed in depressions left by melting permafrost or by chunks of ice left behind by the retreating glacier.