The teaching of courses connected with or related to the study of geology or affiliated or associated subjects by the State Geologist or Assistant State Geologist shall be permitted only during such time as will not unduly interfere with their employment with the State Geological Survey of Alabama or with the State Oil and Gas Board and such teaching shall be limited to courses which require not more than an aggregate of six hours of resident classroom teaching per week. Such teaching shall be permitted during regular scholastic terms, summer school courses or classes for special students as provided by the curricula of the University of Alabama.