Nature Notes: Gift of the Glacier

Long Island has some mammoth glacial erratics
Glacial erratics off Navy Beach in Montauk. Matthew Charron

There are two Stony Hill Roads on the South Fork, one in Amagansett in East Hampton Town, the other in Noyac, in Southampton Town. How did they get their names? By chance? No! They got their names because of the presence of boulders left by the receding glacier more than 15,000 years ago.

Geologists early on termed these boulders glacial erratics. They were deposited here errantly by the last glaciation. Take a ride through Pennsylvania, the northern Midwest, or the northwest of California and you will see a trail of glacial erratics, some as big as a barn, all from the same receding Wisconsin glaciation as it melted away to the north under the influence of a long-lasting warming trend, a trend, mind you, that lately has been picking up speed under the influence of global warming.

Long Island has some mammoth glacial erratics. Much too enormous to be moved by modern earthmoving equipment, they have remained in place where they came to rest after being deposited by the glacier. We don’t see those that are still covered by earth, only the ones that rise out of the earth or rest on its surface. Many are still on land, and many are fully submerged or partially submerged by the marine waters of Long Island Sound, the Peconic Estuary, and by Block Island Sound and the Atlantic Ocean around Montauk.

Lion Head Rock is just one of those many that sit in Gardiner’s Bay, Split Rock sits beside an old trail through Montauk’s Hither Woods, Jason’s Rock reaches up between Bull Path and Two Holes of Water Road in Northwest, and two enormous ones sit in western Southampton Town, one near Stony Hill Road in Noyac, the other south of Great Hill Road in North Sea. My favorite large glacial erratic is the one that sits on the east side of Springy Banks Road, where Hand’s Creek Road enters from the west. It is accompanied by a large lop tree, a white oak, well more than a hundred years old, and the two represent a kind of monument to early East Hampton and the Duke Estate.

The waters in and around Sag Harbor sport an array of large erratics. A bunch lie in plain view during low tide in the shallows of the Sag Harbor inlet on the east side of North Haven. A big one that has become a favorite perch for double-crested cormorants sits in Sag Harbor Cove south of Long Beach Road, where Short Beach Road begins. Since almost all of these erratics are hard rock, such as granite, in composition, they erode very slowly. Where there is a crack in one such as that in Split Rock, trapped water when it freezes can widen a narrow slit into a gaping fissure over time.

Skin or scuba dive in the waters off Montauk and you will find that the glacial erratics reach far offshore, especially the ones that you don’t see from the beach. The glacier that created Montauk reached a couple of miles offshore. Montauk is a mere ribbon of what it used to be. Old Montauk is underwater, both on the south and on the north. Surfcasters use the same exposed erratics over and over again — one might say they own the ones they stand on. The underwater parts of these half-submerged boulders are often covered with barnacles and seaweeds. In other words, they are micro-marine habitats.

Lichens often cover more than half a given erratic’s surface. They are mostly gray-green in color, but occasionally an orange, yellow, or white one is found. They can be very old, as they spread very slowly. Mosses and even ferns can often be found growing in a large erratic’s cavities that have collected a little soil over time. In an age when one fad follows another in short order and fashions come and go in the wind, it is comforting to pass a large erratic by the side of the road or on a trail and know that it is almost ageless, at least as old as Long Island itself.

You won’t find any glacial erratics along the southern part of the South Fork west of Montauk and well south of the terminal (or Ronkonkoma) moraine, except in a few spots where the ice sheet almost reached to the ocean, as at Kellis Pond in Bridgehampton. The ocean beaches from Napeague to the Rockaways are sandy, not stony.

If you walk along a north-south transect, say in Water Mill or Bridgehampton, from the moraine south, you will find that the rocks and stones get smaller and smaller and then disappear altogether. The south half of the South Fork is made up of rich sandy soils, perfect for cultivation. Hardscrabble, a place name for the land south of the moraine reaching to East Hampton Airport, is one of those in-between spots where the sandy soils have a mixture of stones and sand — not prime agricultural land for cultivation.

Where railroads and paved roads have been built and maintained over the years, the once-visible erratics have been removed. In some spots within the last 50 or 60 years, some glacial erratics have been decorated with paint. A few have been carved into. But most of them are in good shape, even in back and front yards, such as along Alewife Brook and upper Springy Banks Roads, where they soften the residential landscape.

There is an old saying that a naturalist steeped in fauna and flora eventually becomes a geologist, and I find myself on that route in later life. The birds and mammals come and go, but the glacial erratics are more permanent, as in the rest of geology. Long Island mostly came from the north by way of glaciers: You have to drill a hole a thousand feet deep in Montauk to reach bedrock, but in New York City you can dig down a few feet and find it.

On Long Island, unlike state-protected tiger salamanders and federally protected sandplain gerardia plants, glacial erratics are not protected by any federal, state, county, town, or municipal statutes. Is that because they are almost timeless in our eyes? Primordial, so to speak? We hate it when a large oak, seemingly almost as timeless, is cut down for a residence or killed by a gypsy moth infestation. In a sense, glacial erratics protect themselves. “They don’t need no stinkin’ badges,” as the saying goes, at least not within our lifetime.


Larry Penny can be reached via email at