INJURED EMPLOYEE WAS OPERATING DOZER PUSHING COAL INTO #3 SECONDARY FEEDER WHEN A ROCK FLEW OUT OF THE SECONDARY STACKING TUBE DOOR THAT FEEDS DIRECTLY INTO #3 FEEDER. ROCK WENT THROUGH THE D OOR GLASS AND STRUCK OPERATOR ON THE RIGHT SHIN JUST ABOVE THE EMPLOYEE'S BOOT CUTTING HIS RIGHT LEG REQUIRING 3 SUTURES.