EE WAS STANDING IN THE CONVEYOR OF A SHUTTLE CAR ATTEMPTING TO UNFOUL A ROCK THAT WAS TOO WIDE TO PASS THROUGH TO THE DUMPING END OF THE CAR. HE WAS USING A SLATE BAR TO TRY TO MANUEVER THE RO CK FREE WHEN HE SUDDENLY SLIPPED, FALLING TO HIS KNEES. WHEN HE FELL HE CAUGHT HIMSELF WITH HIS LEFT HAND, JAMMING HIS LEFT THUMB AGAINST THE CONVEYOR CHAIN.