§ 3018. Revocation of certificate by district superintendent. A district superintendent shall examine any charge affecting the moral character of any teacher within his district, first giving such teacher reasonable notice of the charge, and an opportunity to defend himself therefrom; and if he find the charge sustained, he shall annul the teacher's certificate, by whomsoever granted, and declare him unfit to teach; and if the teacher holds a certificate of the commissioner of education or of a former superintendent of public instruction or a diploma of a state college for teachers or state teachers college, he shall notify the commissioner of education forthwith of such annulment and declaration.