Stones That Traveled: Glacial Erratics, Deep Time, and the Stories They Leave Behind

Glacial erratics are immigrant stones—carried south by ice, dropped without explanation, and left behind to challenge our sense of permanence, place, and deep time.

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MichaelStephenWills

There are rocks that merely sit where gravity has placed them, and then there are rocks that arrive with stories already embedded—foreign syllables carried south on ice, dropped without explanation, and left for us to puzzle over. Glacial erratics belong to the second category. They are migrants with no passports, refugees of deep time, whose presence quietly contradicts the landscape that hosts them.

Long before anyone reached for a hand lens or an ice-flow diagram, people answered such contradictions with imagination. In Ireland, a boulder perched just so on a mountain side is not a geologic problem but a resting place. Leprechauns, we are told, favor such stones—high enough to observe human intrusion, solid enough to outlast it. Skepticism, as folklore reminds us, is not always a stable position. Kevin Woods—better known as McCoillte—found that out the hard way when doubt collided with experience on the slopes of Slieve Foye. What followed was not merely a conversion story, but an act of modern mythmaking: folklore translated into bureaucracy, imagination petitioning regulation, and “The Last Leprechauns” entering the unlikely language of conservation. Stone, story, and belief hardened together into something oddly durable.

Rocks such as this are a favorite perch for leprechauns to rest and contemplate the works of man who have invaded their world. Inhabitants of Carlingford who wander Slieve Foye have come upon them often enough, their stories and certitude in the existence of the Little People are resistant to manifold doubters with their reasons and arguments. Kevin Woods, aka McCoillte, was a doubter until worked on a stone wall on property he owned on Ghan Road, Carlingford. His belief did not arise on the discovery of the leather purse, covered with ages of dust and lime, nor with the gold coins inside. McCoillte pocketed the coins for luck. As luck would have it, McCoillte loved to walk on Slieve Foye. It was on one such walk he and his dog encountered Little People who paralyzed them to escape. His unexplained absence led to troubles with the wife. This experience brought McCoillte around to enough of a belief that he, with lots of help, succeeded in petitioning the E.U. European Habitats directive to recognize leprechauns a protected species. A reserve was establish on Slieve Foye to protect the “Last Leprechauns” and you can google this phrase to learn more about McCoillte’s stories.

Back in the Finger Lakes, we tend to use a different grammar when confronted by an out-of-place rock. We name it, classify it, and trace its lineage northward. Erratics scattered across Tompkins County are geological sentences that begin somewhere else entirely. The bedrock beneath Ithaca—Devonian shale and sandstone—cannot account for crystalline intruders left behind like forgotten punctuation marks. These stones speak of ice sheets thick enough to erase valleys and decisive enough to transport mountains in fragments.

Some of those fragments have been domesticated. Cornell, for example, has never been shy about rearranging its stones. An unremarked erratic along the Allen Trail may once have been shrugged off as inconvenient rubble, while another—dragged from the Sixmile Creek valley—was carved into a seat and made eloquent. The Tarr memorial boulder, resting near McGraw Hall, transforms erratic stone into deliberate monument. It invites rest, contemplation, and perhaps gratitude for those who taught us how to read landscapes written by glaciers.

We find boulders of crystalline rock, commonly derived from Adirondack sources, left behind on the surface of ablation moraine, in the Finger Lakes Region. Cornell finds some and move them, maybe the case for this unremarked erratic found along the Allen Trail of FR Newman Arboretum. Another enormous erratic, brought in from the Sixmile Creek valley, was carved into a seat as a memorial to Professor R.S. Tarr who deciphered much of the glacial history of the Finger Lakes Region. Find it at the southwest corner of McCraw Hall on the Cornell University Campus. Reference: “The Finger Lakes Region: Its Origin and Nature,” O.D. von Engeln, Cornell University Press, 1961 page 106

Glacial Erratic, Fillmore Glen

Elsewhere, erratics remain defiantly themselves. In winter, one along Fall Creek alternates between anonymity and revelation, depending on whether snow smooths its surface or retreats to expose lichen constellations. Bridges pass overhead, traffic flows, semesters turn over, yet the rock remains unimpressed. It has already endured pressure sufficient to rearrange its crystals; a passing academic calendar is not likely to trouble it.

Glacial erratic with and without a snow covver and spotted by lichen along Fall Creek in a winter afternoon as seen from Cornell Botanic Gardens. That is the bridge over Fall Creek on Forest Home Drive. Cornell University, Ithaca, Tompkins County, New York State

Closeup of the same boulder

This boulder, a glacial erratic, was found near Fall Creek and the Cornell Botanic Gardens Horticulture Building. Cornell University, Ithaca, Tompkins County, New York State

This rock, a glacial erratic, was found near Fall Creek and the Cornell Botanic Gardens Horticulture Building. Cornell University, Ithaca, Tompkins County, New York State

Then there are the stones that confront us most directly—those we stumble upon in fields, pulled from soil by plow or frost, demanding explanation. A white, iron-stained marble boulder in a Tompkins County field is not subtle about its foreignness. It does not belong to the local vocabulary of shale and sandstone. Its pale surface, crystalline texture, and mineral scars point insistently north, toward the Grenville terrane of the Adirondack Lowlands. The Balmat–Edwards–Gouverneur marble belt offers the most persuasive origin story: metamorphosed carbonate rock carried south by Laurentide ice, released when climate and physics finally lost patience with one another.

I found this white marble erratic in a Tompkins County field. The highest-probability source is Grenville marble from the NW Adirondack Lowlands / St. Lawrence County (Gouverneur/Balmat–Edwards marble belt), delivered by southward-flowing Laurentide ice. I say the most probable source is metamorphosed carbonate (marble) from the Grenville terrane to the north—especially the northwest Adirondack Lowlands / St. Lawrence County marble belt (the “Gouverneur Marble” and related Grenville marbles), transported south by the last Laurentide ice sheet. Why that’s the best bet: Ice-flow geometry favors a northern source. In the Finger Lakes, glacial ice advanced with a flow direction that was very close to due south, guided by the north–south bedrock valleys. Tompkins County erratics are “exotic” imports. Local bedrock around Ithaca/Tompkins is Devonian shale/sandstone, but the region contains many nonlocal (“exotic”) glacial erratics carried in from much farther north (including southern Canada and beyond). Marble isn’t local to the Ithaca area, but it is abundant in the NW Adirondack Lowlands. The Balmat–Edwards/Gouverneur area in St. Lawrence County is a classic Grenville Lowlands district with marble belts (the same province that yields cream/white building marble around Gouverneur).

What makes this particular erratic compelling is not just its provenance, but the improbability of its journey. Ice moved with purpose here, flowing south along bedrock valleys like Fall Creek and Cayuga troughs, turning the Finger Lakes region into a conveyor belt for distant geology. When the ice melted, it left behind evidence that refuses to blend in. Erratics are geological truth-tellers. They announce that this place was once unrecognizable, that what seems permanent is merely provisional.

Perhaps that is why folklore clings so naturally to stone. Whether leprechauns or Laurentide ice are credited, erratics insist on a larger frame of reference. They ask us to imagine landscapes in motion and beliefs under revision. A boulder can be a seat, a marker, a perch, or a puzzle—but never merely background. It waits, quietly confident, for us to catch up to its story.

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22 thoughts on “Stones That Traveled: Glacial Erratics, Deep Time, and the Stories They Leave Behind”

    1. Maggie, it really is—those misplaced boulders feel like quiet proofs of deep time at work. I love how erratics turn an ordinary landscape into a geological story, reminding us just how dynamic and surprising nature can be. How are the glaciers closer, Maggie?

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    1. Sheree, that’s such a generous compliment—thank you. I’m especially glad the piece rekindled those old geography lessons and let the science breathe a little. When geology becomes story, it feels less like facts to memorize and more like time speaking.

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      1. You are welcome, Michael, my sister and I had a nice hike this morning in the Red Rock Canyon area just west of the city. We stood there in silence amazed at how small we felt!

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  5. Hello Michael,
    Apologies for being ‘out of the loop’ – we always look forward to your articles. Beautiful images with information about the deep history of the land. Your explanation about glacial deposits is accessible and interesting, even for non-Native English followers☺️ Seeing the images around the Finger Lakes makes us fondly remember visiting around this time last year. All our best wishes to your wife and lovely grandchildren. And as always, thank you for sharing.

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    1. Takami, thank you—what a generous and thoughtful note. I’m especially glad the piece felt accessible; glacial stories belong to everyone, not just specialists. It makes me smile that the Finger Lakes images brought back time at Sapsucker Woods last year. Your kind wishes for Pam and the grandchildren mean a great deal to us. Please pass along my regards to David.

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  6. Love the glacial landscape and all the erratics that have been left behind, leaving clues from the past of how the landscape once looked. Beautiful set of captures to showcase some of the erratics you’ve come across.

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    1. Linda, thank you—what a perfect way to put it: “clues from the past.” That’s exactly how these erratics feel to me too, like quiet evidence left behind by past ice ages. I’m so glad you enjoyed the set and the way they tell a bit of that story. Your encouragement is always appreciated.

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  7. When we lived in Scotland our neighbor who was building a house discovered a huge blue glacial erratic as he was digging the foundations. He had to get specialists to help remove it. All of the neighbors helped by taking beautiful blue stones for their rockeries.

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  8. This was fascinating to read, so poetic and thoughtful. I love how you wove geology, folklore, and deep time together and made rocks feel alive with stories. Definitely one of those posts that makes you pause and look at the landscape a little differently.

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    1. Thank you, India Safaris—your comment means a great deal, especially as a first visit. I’m glad the piece made the landscape feel a little more alive. I also spent some time on your well crafted site—beautifully curated, in both the images and the writing. I appreciate you taking the time to read and respond.
      —Michael

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      1. Thank you so much, Michael, that truly means a lot. I’m really glad we found each other’s work. Your writing has a way of slowing time and sharpening how we see the world, and I’ll be reading along with great interest.

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  9. Another beautifully woven piece, Michael. Carrying me from leprechauns on Slieve Foye to Adirondack marble in Tompkins County—folklore and glacial history sit side by side without diminishing either. I love learning a bit more about nature and the world with your posts, as your description of erratics as ‘geological truth-tellers’ feels exactly right—they really do expose how provisional our sense of place and permanence is. The mythical journey the white marble boulder from the Grenville terrane took, and your writing, slows me down and sharpens my eye—I’ll be looking at every out-of-place boulder on my hike this afternoon 😊!

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    1. Dalo, thank you for such a generous and thoughtful reading. I’m glad the balance between folklore and glacial history came through—that’s exactly what I hoped for. If the piece slowed you down and sharpened your eye, that’s the best reward. May your hike reveal at least one wonderfully out-of-place boulder.

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  10. I remember a line of glacial activity in northeastern Montana. North of the line, the surface of fields continue to receive ancient stones, but the land is quite fertile. South of the line, one finds far fewer rocks, and the soil is less fertile.

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    1. Richard, that’s a wonderful observation—and a perfect illustration of how ice continues to write on the land long after it’s gone. The contrast you describe between stone-rich, fertile glacial till and the leaner soils beyond the ice’s reach says so much about deep time at work. I love how your Montana example grounds the story of erratics in lived landscape. Thank you for sharing that perspective.
      —Michael

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