Apparently more than just valuable artwork is missing from the Boston Public Library's archives.

A library spokeswoman says a retired employee who now volunteers told administrators last week that gold coins originally placed in the cornerstone of the main building have been missing for decades.

The spokeswoman said the library has informed police.

The coins were apparently placed in an 1888 time capsule that was opened in the 1990s. No estimate of the coins' value was disclosed.

Police and the FBI are investigating the disappearance of two pieces of artwork worth more than a half million dollars combined. A top employee has been placed on leave.

It's unclear whether the missing art pieces, a 1634 Rembrandt etching and the 1504 Durer engraving, were stolen or simply misfiled.