Scientists and volunteers involved in an archaeology project along the Patuxent River this month discovered shells thought to be used by African slaves who worked the fields of white colonists in the 18th century.

Cowrie shells, small white shells from the Pacific and Indian oceans, were historically used by Africans as currency, worn as jewelry and sewn into clothing. They were found on the former site of the family home of Richard Smith Jr., a militia captain and surveyor general for the Maryland colony, on the grounds of the Jefferson Patterson Park and Museum in St. Leonard. Of particular interest to the archaeologists is a shell that is filled with lead and affixed with a metal eyelet, as if to be used as a button.

"That is very unique," said Julia A. King, director of the Maryland Archaeological Conservation Laboratory, which is located at the park in Calvert County. "So far we haven't been able to find someone who has one like it."

The excavation of the site began in 1999, and three years later, volunteers were allowed to participate as part of a public archaeology program. This year, the public field sessions ran from May 17 to June 30.

Before the Maryland Constitution outlawed slavery in 1864, the use of slave labor was common throughout Southern Maryland at farms growing tobacco, wheat and corn. On an inventory of the Smith house, which was built in 1711, 30 to 40 slaves were listed, King said.

A good deal of information about the site came to light because of a property dispute between the Smith family and neighbors. As part of the court proceedings, maps and documents were made detailing the locations of buildings, which has helped researchers analyze what they unearth.

The shells were found near what remains of the brick foundation of the Smith house, not particularly close to the site of what is believed to have been a slave cabin, less than 200 feet away. The proximity of the shells to the main house raises questions about the social interactions between blacks and whites at the time, said Eric Frere, crew chief for the excavation.

During the 22-year history of the Jefferson Patterson Park and Museum, researchers have investigated more than 70 archaeological sites on the 560-acre property, documenting the lives of Native Americans, Colonial settlers and African American slaves. The museum also serves as a repository for the historical artifacts of many government agencies and institutions, including the Patuxent River Naval Air Station. It houses a collection of about 7.5 million artifacts, said Michael A. Smolek, the museum's executive director.

Inside the 38,000-square-foot Maryland Archaeological Conservation Laboratory are massive overhead cranes capable of moving heavy artifacts, such as a 300-pound cannonball found at the bottom of the Baltimore Harbor.

On Friday, a rudder from an early 20th-century canal boat from Canal Place in Cumberland was submerged in a polyethylene glycol solution. Smolek said the solution would strengthen the cell walls of the wood. After that bath, the rudder would be solidified inside what he described as the largest freeze-dryer in North America.

"This is a production lab," Smolek said. "We're here to produce preserved artifacts."

In another bin was a portion of an iron stove from Jamestown, the first permanent English colony in North America. The stove was being repaired after saltwater damaged it during Hurricane Isabel. Down the hall, a Colonial-era dugout canoe built by African Americans on the Eastern Shore was being reassembled.

Among the most famous artifacts in the museum, Smolek said, is the helm off the CSS Alabama, a Confederate sloop-of-war that spent two months ravaging Union ships in the North Atlantic before being sunk in 1864. Captained by Raphael Semmes of Charles County, the Alabama sank dozens of Union vessels during the Civil War, Smolek said.

"She was a screaming-fast vessel; she was steam as well as sail," he said. "She was a real killer."

The laboratory, which is open to the public the first Friday of each month, recently received a grant from the National Endowment for the Humanities to put all of its historical records into an electronic catalogue. King said the project may start in September and is expected to take about two years.

"These artifacts actually belong to the citizens of the state," King said. "They're in very secure locked rooms so they won't get lost or misplaced, but they do belong to the citizens. They should be seen."

Eric Frere, crew chief of the excavation, shows where cowrie shells thought to be used by slaves were found.This cowrie shell, affixed with an eyelet, is of particular interest.A Colonial-era dugout canoe built by African Americans on the Eastern Shore is being reassembled at the Maryland Archaeological Conservation Laboratory. Artifacts from around the region are brought to the lab to be preserved.