THE DUMP TRUCK WAS BEING LOADED WITH SHOT ROCK &WHEN IT TURNED THE BUCKET OVER TO DUMP INTO THE TRUCK BED THE ROCK BOUNCED OFF THE CAB SHIELD & ROLLED OVER ONTO THE CAB OF THE TRUCK. AS THE RO CK FELL THE CAB ROOF BEGAN TO CAVE SLIGHTLY CAUSING THE DRIVER TO QUICKLY MOVE TO THE LEFT TO AVOID BEING HARMED, POSSIBLY AGGRAVATING A PREVIOUS INJURY (HE REPORTED NUMBNESS A FEW DAYS LATER