I'm not sure that embedding significant items in cornerstones is as common as it once was. At one point it was often done on significant (and not-so-significant) buildings.
One of the former would be the U.S. National Archives building in Washington, D.C. President Herbert Hoover participated in the ceremony. The ceremony was considered important enough that President Hoover moved the ceremony earlier (before it actually was time to lay the cornerstone) so his name could be on it.
I'm sure most who read this blog know that there are many voices today proclaiming that our nation has no significant religious or Christian roots. Someone forgot to tell President Hoover and the others who set up this ceremony, apparently, because the object placed in the cornerstone included:
- A Bible
- copies of the Declaration of Independence and the Constitution
- an American flag
- copies of the public acts authorizing the construction of the building
National Archives Website