DALLAS — Dallas Cowboys defensive tackle Josh Brent has been jailed in North Texas after failing a second drug test.Court records in Dallas County show Brent tested positive for marijuana in a urine test last week. The positive result violates of bail conditions imposed after he was charged late last year with intoxication manslaughter. Brent failed an initial drug test in May. He’s being held without bail pending a hearing July 19.Authorities say Brent was driving Dec. 8 when he had a wreck, causing the death of Cowboys practice squad player Jerry Brown. They say Brent’s blood-alcohol level was more than twice the limit of .08. His attorney, George Milner, was not immediately available for comment Thursday.