OPERATING A BOLTER IN A FLUSH FACE AREA, THE MACHINE WAS LOCATED OUT IN THE INTERSECTION WHICH WAS AN OVERCAST HOLE. HE WAS INSTALLING THE FIRST BOLT UNDER THE BROW, STANDING OUT IN THE OVERCA ST HOLE AREA. A SMALL ROCK FELL FROM THE ""HIGH ROOF"" AREA STRIKING HIS LEFT THUMB. THE INITIAL DIAGNOSIS WAS A HAIRLINE FRACTURE TO THE THUMB.