The items are well-preserved because they were found below the water table, which protected them from contact with air. The well is a virtual time capsule, according to archaeologists at Historic Jamestowne.
A child?s leather shoe, surgical tools, buttons, untarnished copper, nuts and seeds, including a tobacco seed, have been unearthed. Above the water level, a German jug, weapons, ceramics, beads and large quantities of butchered animal bones and seafood remains have been found. Items include clam, mussel and scallop shells; fish bones; dorsal plates from Atlantic sturgeons ; crab claws; and barnacles."
I'm sorry I didn't have time to explore Jamestown when I visited Williamsburg several years ago.