OPERATING THE TRACK LOADER OVER A BERM 3'HIGH INTO A DRAINAGE DITCH WHEN LOADER WENT OVER BERM. THE FRONT END HAD A SUDDEN DROP WHICH THREW THE OPERATOR FORWARD INTO THE CAB. OPERATOR HIT FOREHEAD ON THE REAR VIEW MIRROR MOUNTED IN THE CAB. THE ONLY DAMAGE WAS TO THE MIRROR, WHICH WAS BROKEN. EE WAS WEARING HIS SEATBELT.