ARLINGTON, Texas -- The Dallas Cowboys' new $1.15 billion stadium would probably be off-limits for undergroumd drilling under the team's contract with the city of Arlington.

City Attorney Jay Doegey told The Dallas Morning News that drilling could affect the building's structural integrity. The language in the contract was added before five small earthquakes shook Cleburne, a town 50 miles southwest of Dallas.

Researchers are examining whether those earthquakes were caused by gas drilling in the underground Barnett Shale formation.

The towns sit upon the Barnett Shale, a geologic formation that is perhaps the nation's richest natural gas field.