EMPLOYEE WAS OPERATING THE D6H DOZER IN A STRIPPED AREA OF THE QUARRY. HE WAS HEADING EAST WHEN HE INADVERTENTLY DROVE OVER A 1 1/2' LEDGE. THE DROP CAUSED HIM TO BOUNCE IN THE SEAT STRIKING H IS HEAD ON THE ROOF OF THE DOZER CAB, CAUSING PAIN IN HIS LOWER NECK.