THE EMPLOYEE WAS SITTING IN THE CAB OF THE 9 CATTRUCK THAT WAS BEING LOADED WITH SHALE BY AN ENDLOADER IN THE QUARRY. A LARGE PIECE OF SHALE FELL OUT OF THE ENDLOADER BUCKET INTO THE BED OF TH E EMPTY TRUCK, CAUSING IT TO BOUNCE AND THE OPERATOR TO BE THROWN AROUND THE CAB, INJURING HIS BACK.