Go in one piece Forest in New England, and chances are you – almost literally – will stumble upon a stone wall. Perhaps it’s thigh high and cobbled together with stones of various shapes and sizes, with lichen patches and spongy moss instead of mortar. Most stones are referred to as “two-handed” – light enough to lift, but not with just one hand. The wall winds down a hill and cannot be seen. According to Robert Thorson, a landscape geologist at the University of Connecticut, these walls are “almost everywhere” in the woods of rural New England.

He estimates that there are disused stone walls more than 100,000 miles old, or enough to orbit the globe four times.

Who would build a stone wall in the middle of the forest, let alone hundreds of thousands of kilometers from them? Nobody. The walls were not built in the forest, but in and around farms. By the middle of the 19th century, over 70 percent of New England had been cut down by settlers, a hilly landscape of small farmers as far as the eye can see. By the end of the century, industrialization and large-scale farming resulted in thousands of fields being abandoned to initiate a slow process of reforestation.

“New England had great pastures,” says Thorson. “It was a beef-butter-bacon economy.”

When the farmers cut down these New England forests, they found stones – many, many of them. The glaciers that receded at the end of the last Ice Age left behind millions of tons of stone of various sizes. New England soils are notoriously rocky to this day.

Stone walls in Block Island, Rhode Island, c. 1880. Block Island Historical Society, printed by Robert Downie

When life gives you stones Build a wall. The farmers pulled these plow-inhibiting stones from their fields and piled them around the edges. “The farmer’s main interest was his fields,” says Thorson. “The walls are just a waste heap. It was routine farm work. “This process has been repeated on thousands of farms in the area – a collective act of work on a glacier scale.

The supply of stone seemed endless. In the fall a field would be cleared and in the spring there would be a whole new crop of stones. This is due to a process called the “frost lift”. When deforested soils freeze and thaw, stones shift and migrate to the surface. “People in the northeast thought the devil had brought them there,” says Susan Allport, author of Sermons in Stone: The Stone Walls of New England and New York. “They just got on.”

Stone wall at Old Manse, Concord, Massachusetts. Robert Thorson

The construction of the Wall peaked in the mid-19th century when Thorson estimates there were around 240,000 miles of it in New England. That’s roughly 400 million tons of stone, or enough to build the Great Pyramid of Giza – more than 60 times that.

Nobody is more devoted to pondering these walls than Thorson, who has written a children’s book, field guide, and countless articles about them since he first moved to New England in 1984. Thorson, bald and bearded, a mossy stone himself, is a landscape geologist and clearly remembers his first walks in the forests of New England – one stone wall after another. His mind was full of questions about what they were and who built them. “It was an extraordinary phenomenon,” he says. “One thing led to another, and I was obsessed with the subject.”

Thorson started the Stone Wall Initiative in 2002 to educate the public about this specific feature of their forests, to preserve the walls, and to study how they affect the landscape around them. Thorson has built a reputation as the ultimate expert on this phenomenon. “Do you know how a natural history museum would have a person identifying things for you? I’m the stone wall guy, ”he says.

Robert Thorson with a stone wall, Kettle Pond National Wildlife Refuge, Rhode Island. Liam nibbles

Every year he takes his students to a maple-beech forest stand in Storrs, Connecticut that he calls “The Glen” to see a classic stone wall on a farm. This wall is thigh high and consists mainly of metamorphic gneiss and slate rocks that are common in the valley flanks of central New England. With Thorson’s help, one begins to see a small structure in the way the stones were stacked – in messy layers by a farmer who added a load at a time.

Thorson may be particularly obsessed with the walls, but he’s not alone in interest. He is constantly invited to speak at garden clubs, historical societies, public libraries, and more. “Interest is not waning,” he says. “Twenty years later it’s still going on.”

His field guide, Exploring Stone Walls, is a directory of some of the most unusual, interesting, or distinctive walls in the area. The tallest example is a mortar wall under the Cliff Walk in Newport, Rhode Island, which measures over 100 feet. The oldest wall in Popham Point, Maine dates back to 1607. Thorson’s most popular historically significant wall is in the Old Manse, a historic home in Concord, Massachusetts. It provided cover for Minutemen who fired on the British during the War of Independence. Thorson also highlights Robert Frost’s Mending Wall, located on his farm in Derry, New Hampshire, which is the inspiration for the famous “Good Fences Are Good Neighbors” line.

The “mending wall” on Robert Frost’s Farm in Derry, New Hampshire.
Robert Thorson

Thorson knows as much as one can know about the Wonders of the World of the Walls in the northeast, but much remains to be learned, especially what they mean for ecosystems, such as their role as a habitat and barrier to wildlife and their impact on erosion and sedimentation. “It sounds silly,” he says, “but we know next to nothing about her.”

The geographer and landscape archaeologist Katharine Johnson did her PhD in mapping stone walls from above using lidar technology (light detection and distance measurement). Lidar is similar to radar, but uses light instead of radio waves to detect objects. Laser pulses – thousands per second – are emitted from a specially equipped level. There are so many of these impulses that some are able to hit the tiny spaces between the leaves and penetrate to the forest floor, even through thick tree cover. Johnson’s lidar images show the scope of these intersecting stone walls in a way that nothing else can.

A lidar image showing the hidden walls beneath a forest in Eastford, Connecticut. USDA NRCS, CTECO, Katharine Johnson and Will Ouimet

Her research shows that the walls, freed from the region’s resurgent forests, provide a snapshot of 19th century history – a map of which land was cleared and farmed at the time. Combined with other data on the forests themselves, this can help professionals model historical forest cover and, in turn, help ecologists understand how forests regrow after complete disruption or clearing. The walls can hold the key to New England’s social history, including settlement patterns and farming styles. They provide a static background against which changes can be measured.

“Stone walls are the most important artifact in rural New England,” says Thorson. “You are a visceral connection to the past. They are certainly a holdover from an earlier civilization like a ruin in the Amazon rainforest. “

Each of the millions of stones that make up the stone walls of New England was held by a person, usually a subsistence farmer or perhaps a hired Native American or slave. What remains is a trace of innumerable individual actions engraved on the landscape. “This work,” says Allport, “continues hundreds of years later.”

The NH Stone Wall Mapping program is an online project that enables people to identify stone walls through LIDAR images of the area. From that moment on, they have found 12,700 miles of walls across New Hampshire. (I wrote about the project a year ago)

(Only Strafford County on the seashore has very few walls. I wonder if this is a function of the type of agriculture that was practiced there, the type of rock found there, or just an accident of who attended.)

It is not clear how many miles of stone walls exist in the state. The best estimate I’ve made is for the whole of New England and New York State of about 250,000 miles in 1871 when agriculture changed, largely because railroads made it possible to move food from the Ohio River Valley to the east coast . So the farmers moved west to more fertile soil. After that, relatively few walls were built and many were torn down or moved.

My guess is that New Hampshire had at most a fifth of those walls from 1871, which would be 50,000 miles. So we are a quarter of the way there!

Note that these walls have not been confirmed on the floor. They have been identified by their appearance on LIDAR. So we shouldn’t focus too much on numerical details: I’m sure that some of the “walls” found are actually old roads or earth benches or other false positives.