INJURED HAD HELPED REMOVE ROCK FROM THE MOBILE BRIDGE CONVEYOR. HE WAS POSITIONED LOOKING TOWARD THE OUTBY DUMPING POINT OF THE MBC WITH HIS HAND LOCATED ON TOP OF THE MBC, JUST ABOVE THE CONVEYOR THROAT. A LG. ROCK CAME DOWN THE CONVEYOR AND STRUCK INJURED ON THE TIP OF SMALLEST FINGER OF THE RT. HAND.