TWO EMPLOYEES HAD JUST FINISHED BOLTING THE FACE OF #4 ENTRY. THEY BACKED THE BOLTER UP NEAR THE LAST OPEN CROSSCUT. ONE GOT OUT OF THE OPERATOR CAB AND WAS WALKING TOWARD THE FACE WHEN A ROCK 34"" LONG X 20"" WIDE X 5"" THICK FELL OUT OF THE ROOF BETWEEN BOLTS AND STRUCK HIS FOREHEAD BELOW THE BILL OF HIS HARD HAT CAUSING A CUT & SLIGHT CONCUSSION (HE WAS LOOKING UP AT THE TIME).