EMPLOYEE WAS INSTALLING CHAIN HANGERS IN THE BELTLINE OF UNIT #4. HE WAS STANDING NEXT TO THE BOLTER PUSHING THE ATRS AGAINST THE MINE ROOF WITHTHE CONTROLS. A ROCK FELL OUT OF THE ROOF STRIKI NG HIS SHOULDERS THEN SLID DOWN HIS RIGHT ARM HE SUSTAINED A CUT ON HIS ARM JUST BELOW THE ELBOW.