Just read this fun fact in Time magazine - in 1825 John Quincy Adams was sworn-in as the sixth President of the US not on a Bible but on a book of laws instead.

For more information, here's a snippet from a 2007 article from the Department of State's America.gov website: "U.S. Swearing-in Ceremonies Highlight Religious Freedom Legacy".

Because America has been predominantly Christian, it became customary, but not mandatory, for U.S. presidents and other public officers to carry or place their hand on the Bible while taking the oath of office. Fiercely secular, John Quincy Adams took his oath on a book of laws containing the U.S. Constitution. Theodore Roosevelt used no book at all. Franklin Pierce and Herbert Hoover, a Quaker, did not swear but affirmed the oath of office.

Interesting stuff ...