Trading on the floor of the Nasdaq stock market's Philadelphia Stock Exchange yesterday was halted for an hour because of smoke.

The exchange, known as Nasdaq OMX PHLX, handles options trading.

The Fire Department was trying to determine the origin of the smoke.

Trading was halted at 11:05 a.m. and all smoke had been cleared from the floor by 12:05 p.m. Trading resumed about 35 minutes later, NASDAQ OMX said in a statement. Nasdaq acquired the Philadelphia Stock Exchange, the nation's oldest stock exchange, in July 2008.