OLD DUMP EMPTY TRACK ON TURN, MAN OBSERVED A LOW RAIL ON TURN. HE STOPPED HIS ROCKDUST TRIP AND WAS GOING TO RAISE TRACK AND BLOCK IT. WHEN HE GOT OUT HIS LIFTING JACK, IT WAS PLUGGED WITH MUD. HE TURNED THE JACK OVER AND HIT IT ON STEP OF LOCOMOTIVE TO REMOVE MUD. THE STEM CAME DOWN CATCHING THE MAN'S LEFT RING FINGER BETWEEN THE BASE AND THE FOOT OF THE JACK.