Rare nautical charts from the late 1700s signed by a Vineyard sea captain and depicting the coast of Portugal and the Orkney Islands are among the treasures that have been recovered from what is believed to be the second oldest house on the Island, Sheriff’s Meadow Foundation executive director Adam Moore said this week.

The maps were discovered by artist Laurie Miller above the ceiling in the attic of the Mitchell House on the 156-acre Quansoo Farm in Chilmark, which was bequeathed to the foundation several years ago by Florence (Flipper) Harris. Mr. Moore described efforts to assess the house in advance of restoring it in remarks to the conservation group’s annual summer benefit dinner held Monday at Ashakomaksett Farm in Edgartown.

“We inspected the house last week with historic preservation expert Brian Cooper, and everywhere Brian turned we found something significant,” Mr. Moore told a crowd of about 400 people gathered under a huge tent. “The wrought-iron hardware in the door frame is 300 years old. There are wooden latches from the 17th century. There is plaster made of horsehair and oyster shells and wattle and daub walls made of mud and straw. On the walls there are inscribed names, and dates, and carvings of ships — sloops and schooners and brigs — one after another. The lesson here is that on Quansoo Farm we have a significant historic structure.”

Mr. Moore said later that Sheriff’s Meadow is committed to restoring the house and has determined it will not be used for living quarters, but rather for “some level of historic use.” The foundation hopes to get the house listed on the National Register of Historic Places, and is working with the state and local officials on a preservation plan, he said.

The charts, reproductions of which were displayed at the foundation’s fundraising event, show the coasts of Spain and Portugal, the West Coast of Ireland, the Orkney Isles, and the British Channel and bear the signature of Capt. Samuel Hancock, who is believed to have lived in the Mitchell House with his wife, Frances, and their four children at the turn of the 19th century.

Born in 1773, Captain Hancock became a master mariner and captain of merchant vessels engaged in transatlantic trade. During an eventful career, he served time in a French prison, met his wife in Liverpool, moved to Chilmark and was later briefly captured by the British in the War of 1812 before returning to the Vineyard, where he is buried.

Parts of the Mitchell House date to the 1600s, Mr. Moore said. The only house on the Island believed to be older is the Vincent House, now owned by the Martha’s Vineyard Preservation Trust and used as a museum in Edgartown.

Donated to Sheriff’s Meadow by Mrs. Harris over a period of years beginning more than a quarter century ago, the Quansoo Farm gift is the second largest land bequest in the history of Sheriff’s Meadow.

A lifelong summer visitor to the Vineyard and a resident of Ardmore, Pa., Mrs. Harris was the sister of Polly Hill. She died in June 2005.