EMPLOYEE WAS ROOF BOLTING IN THE FACE OF #3 ENTRY ON UNIT #1. A ROCK 6' X 2 1/2' X 2"" FELL OUT FROM THE ROOF & RIB AND STRUCK HIM ON THE RIGHT ARM AND LEFT SHOULDER. HE RECEIVED A SEVERE LACER ATION TO THE RIGHT ARM AND A HAIRLINE FRACTURE TO THE RIGHT ARM. HE RECEIVED 50 PLUS STITCHES AND A CAST TO HIS ARM.