EMPLOYEE WAS ROOF BOLTING A NOTCH TO THE LEFT. AS HE WAS DRILLING A ROOF BOLT HOLE A PIECE OF ROCK FELL FROM BETWEEN THE ROOF BOLTS STRIKING HIS LEFT SHOULDER AND LEFT HAND. THE INCIDENT FRACT URED HIS LEFT THUMB. EMPLOYEE WILL BE INSTRUCTED TO ALWAYS CHECK THE ROOF AND RIB IN HIS WORK AREA.