INJURED WAS HAULING 8' TIMBERS IN ON A FLATCAR BEING PULLED BY A BROOKVILLE MOTOR. AFTER ROUNDING CURVE, MOTOR HIT A ROCK THAT HAD FELL OUT OF TOP AND WAS LAYING IN MIDDLE OF TRACK. MOTOR JUMP ED OFF TRACK AND WENT INTO BELTLINE. IMPACT BROKE BOLTS OUT OF CANOPY, CAUSING CANOPY TO HIT HIM IN THE HEAD, NECK AND LEFT HAND.