The St. Clair County Sheriff's Office says a bomb threat called into the Carmichael Theatre Chain in Georgia this morning forced the evacuation of the movie theatres at Birchwood Mall.  Sheriff Tim Donnellon says deputies received the call of a bomb threat shortly after 10:00am.  They went to the movie houses at the mall, and with the help of Fort Gratiot Fire Department and Birchwood Mall security, evacuated the theatres.  A Michigan State Police bomb sniffing dog was called in to check the theatres and shortly before 3:00pm this afternoon, the building was cleared and no bomb was found.  The incident originated with a call to the Carmichael Theatre headquarters in Atlanta.  According to local theatre managers, a bomb threat had been called in to the main headquarters by a disgruntled employee, stating there were nine active devices spread throughout the chain of theatres in the United States.  It's unknown at this time how many theatres were involved nationwide and there's also no information at this time on a possible suspect in this incident.