CLAYTON -- Construction workers made an unusual discovery at the future home of Johnston Medical Center of Clayton.Hospital and community leaders held a groundbreaking ceremony for the Clayton medical center June 18. After hundreds of guests left, construction workers discovered a metal vault that was 3 feet deep into the ground near the back of the property. A rotting wooden casket was inside the rusty vault.“The vault had been damaged over years and years of farming out there from tractors,” said Kyle McDermott, head of construction for the hospital. “It was pretty bent and beat up and basically sliced in different places across the top, and it was full of dirt.”Most vaults open from the top, but this vault has a door at one end, McDermott said. “There was a door on one end, and the casket would slide in,” he said. “No one had seen anything like this, which made us wonder to start with, ‘Is this really a casket?’ We thought maybe it was from the Civil War and people used it to store artillery.”Clayton police and the Johnston County Medical Examiner’s Office found bone fragments the following day. The vault, casket and bones has been turned over to the state Medical Examiner’s Office.Officials speculate that the vault dates back to 1890, McDermott said. Testing done on the property before construction found no burial grounds, he said.