The walls of Potato Cave hold a question about Acton's past

A mysterious stone chamber in Acton's Nashoba Brook conservation land that has long fascinated hikers and local history buffs was probably built for food storage by farmers in the late 18th or 19th centuries and not by Native Americans, an archeologist hired by the town said last week.

The view is archeologist Craig Chartier's preliminary conclusion based on incomplete findings in an archeological investigation of the structure.

The Nashoba Brook Chamber, commonly called the Potato Cave, is an underground room nestled into a hillside near the brook. It has a long, narrow entrance passageway, walls of piled rocks, and a roof of huge stone slabs covered with earth.

Late last month, stonemasons cut timbers and temporarily placed them inside the chamber to stabilize it. Then Chartier and volunteers dug into the earth around the structure and sifted for artifacts in search of clues about when the chamber was built, what it was used for, and, at the core of the mystery, who built it.

Some people have theorized that Colonial farmers built the structure as a root cellar, cider storage room, or animal shed. Others have speculated that the native peoples who lived in the area for thousands of years before the first Europeans arrived built the chamber for ceremonial purposes or as a sweat lodge.

Although the digging is not yet done, findings to date have caused Chartier to come down on the side of Colonial or post-Colonial construction.

``It really seems like probably a late 18th- to 19th-century structure, and probably built by someone on the farms in that area," he said. ``It was probably used for some kind of food storage." He didn't specify the type of food.

He said his assessment could change if contrary evidence is found. He said he based his current opinion on artifacts found at the site and a comparison with stone chambers in other parts of New England, especially Vermont, that researchers have determined were built by early farmers of European descent.

Chartier said there are hundreds of stone chambers around the country, including 50 or 60 in one county in Vermont. Locally, residents have reported chambers of unknown origin in Concord, Harvard, Littleton, and Stow.

In the Acton chamber, Chartier said, he found nails from three different periods: a modern nail; a 19th-century nail; and a handmade nail from the 17th, 18th, or early 19th century. ``Someone could have reused old nails," Chartier observed. He said he also found some modern glass, a modern bullet, and a piece of black-glazed red pottery from the 18th or 19th century.

``Anything we find here is significant because it will give us a better understanding of what the structure was used for," Chartier said. ``We'll come up with a best guess at the end. . . . . We'll never know the most complete story, just the best guess we can get."

Chartier also found a Native American spear point, but it was in dirt that had been backfilled and couldn't be used to date the structure. ``It appears Native Americans were using that area 6,000 to 8,000 years ago based on the point we found," he said. He added that artifacts from Native Americans of the same period have been found across town.

This week, a stonemason found some charcoal that could be carbon-dated, helping to pinpoint when the structure was built.

Linda McElroy of the town's Land Stewardship Committee is coordinating the stone chamber project, which will include taking apart and reconstructing wall sections that have partly collapsed. The public is not currently allowed to enter the structure.

The structure is L-shaped, with a low entrance passage leading to a room that is tall enough for most people to stand in. The entrance passage is 3 feet 6 inches wide by 17 feet 5 inches long. The main room measures 11 feet 5 inches by 6 feet 10 inches. Within this room, there is a 2-foot-square pillar made of stacked flat stones.

The project will also include researching the historical ownership of the property, creating informational panels for the site, and putting the artifacts on display, probably at Town Hall.

``I'm happy to have the structure here in Acton and being worked on, whether it is Colonial or pre-Colonial," said Kimberley Connors, a member of Acton's Historical Commission and a trained archeologist who is helping with the project. ``I am happy that Acton is spending the time and money to have it restored. I think it's a great project."

The town is paying for the project with $20,000 in Community Preservation Act funds. The nonprofit New England Antiquities Research Association, which has questioned traditional archeology's attribution of stone structures throughout New England to farmers, is contributing $1,000.

Suzanne Carlson, a preservation architect from Maine, has been involved in the association for years. ``There's an interesting myth . . . that Indians never built anything in stone," she said. ``That myth has become a dogma of sort."

Carlson said she has visited the Nashoba Brook stone chamber several times and has seen hundreds of stone chambers of various designs in New England and New York state.

``This doesn't make sense for food storage," she said, citing the long passage to get to the main chamber. ``I'm not convinced it's Colonial at all. I see absolutely no reason whatsoever that native people could not have built it."

McElroy agreed that there are some puzzling things about the structure. While deferring to Chartier's professional opinion of its origin, she asked, ``Would a European farmer have spent a lot of time moving those gigantic roof slabs? I think he would have been much more likely to cut a few slabs of wood."

Tom Tidman, director of natural resources for the town, said that, regardless of who built it, the chamber ``is historically significant to Acton." He added that people have gone to look at the chamber and been inquisitive about it for generations.

``I must admit, I have been totally in awe of it," said Connors of the Historical Commission. ``It's an impressive structure. Someone spent a lot of time to construct it."

Sally Heaney can be reached at heaney@globe.com.