Waves rush over cobblestones on the coast of Schoodic Peninsula on Nov. 9, near Blueberry Hill in Winter Harbor. Credit: Courtesy of Aislinn Sarnacki

A wave rolled toward us, a growing hill of water that transformed into a turquoise arc before crashing down over the cobblestones. My dog, Juno, lept back as the frothy ocean rushed up the beach to kiss our feet.

Then, in a blink, the water was flowing back the way it had come. Hundreds of smooth, round stones tumbled with it, clacking together to create a most unusual yet soothing sound.

“It’s like those fireworks that crackle,” my sister, Jillian, observed.

I knew just what she was talking about, having shared many Fourth of July celebrations with my sister. They had been among our favorite fireworks as children. But I was puzzled by the association, so I let my mind wander back.

There we were, sitting on the cool grass on the Searsport waterfront. The tang of sparkler smoke hung in the air. Overhead, a firework burst into balls of gold that would sparkle and crackle as they vanished.

I listened to the ocean again, and there it was — the cobblestones, rolling and clattering in the waves. It did sound like those crackly fireworks, plus something else. Prior to that, I’d always likened the sound to rain. Or, more specifically, a rainstick.

Yet there’s something about the sound of waves running over cobblestones that’s utterly unique and wondrous. And it can only be heard on very specific beaches, ones composed of smooth, round stones.

In Maine, we’re lucky to have quite a few cobblestone beaches. Worldwide, they’re considered somewhat rare. Countries with abundant cobble beaches — also known as shingle beaches — include the United Kingdom, New Zealand, the Philippines and Japan, according to a 2017 article written by Dana Hunter for the Scientific American.

These fantastical beaches, composed entirely of round stones, form as a result of glacial activity and big waves.

The cobblestones are often made from durable rocks left behind by glaciers. They’ve been rounded by being continuously tossed about by waves, then trapped in a cove. The powerful waves pull lighter material such as sand, shells and sediment into deeper water, leaving just the round, heavy rocks behind.

“Vigorous waves carry larger cobbles, and as their energy dissipates, smaller stones are dropped,” wrote Hunter. “Some beaches don’t show much variation, as the waves hit them pretty straight on. Others will show a marked gradation, going from teeny tiny pebbles up to large cobbles.”

Waves rush over cobblestones on the coast of Schoodic Peninsula on Nov. 9, near Blueberry Hill in Winter Harbor. Credit: Courtesy of Aislinn Sarnacki

Geologists use different names for rocks based on their size, though there are a few different scales that are used. According to the Udden-Wentworth Scale, a cobble is 64 to 256 milllimeters across, which is larger than a pebble and smaller than a boulder.

In Maine, I’ve visited a variety of cobblestone beaches. Some have more perfectly rounded stones than others. Some have larger cobbles than others. And some have more variety in the color and patterns on the stones than others.

The cobblestone beach that I visited most recently with my sister was near Blueberry Hill on the Schoodic Peninsula. Located in the town of Winter Harbor, the beach was a part of the mainland section of Acadia National Park.

It was a sunny, warm day in November — T-shirt weather, if you can believe it. We’d just hiked the nearby Schoodic Head and decided to wander down to the water to enjoy the waves, which were particularly impressive that day.

The beach, which was really more a jumble of large, spherical stones, was challenging to walk on, especially with a leashed dog. Cobblestone beaches, particularly the ones with large cobbles, aren’t really made for paws. The round stones teeter and tend to pinch toes and nails. So we had to take it slow.

Some other outdoor destinations where I’ve found spectacular cobblestone beaches include Cutler Coast Public Reserved Land in Cutler, Boot Head Preserve in Lubec, Quoddy Head State Park in Lubec and Bog Brook Cove Preserve in Trescott.

Acadia National Park is home to several cobblestone beaches, including an expansive one at the Seawall on Mount Desert Island, and pocket beaches on Isle au Haut. According to the National Park Service website, cobbles are a critical part of Acadia’s shoreline habitat, providing shelter for small animals and a place for larvae to cling onto.

I’ve also traveled farther northeast to find particularly colorful cobblestone beaches at Irving Nature Park in New Brunswick, Canada. If you ever get a chance to drive to the charming city of Saint John, it’s right on the way.

When visiting cobblestone beaches, it’s tempting to select a favorite rock to carry home. After all, they look like petrified eggs — some large enough to belong to a dinosaur. But I urge you to leave them where you find them.

Perfectly rounded cobblestones take a long time to form, and if everyone took one from a beach, it would slowly disappear. A cobblestone perched on a bookshelf is interesting, sure, but it’s far more enjoyable to sit on a beach (or stand, since sitting on round rocks really isn’t that comfortable) surrounded by thousands of them. There you can listen to them tumbling in the waves, making music like a crackling firework.

Aislinn Sarnacki

Aislinn Sarnacki is a Maine outdoors writer and the author of three Maine hiking guidebooks including “Family Friendly Hikes in Maine.” Find her on Twitter and Facebook @1minhikegirl. You can also...