This study assessed the effectiveness of integrating logical thinking skills into a geology course designed for nonscience majors. Goals of the study were to: (1) design a unique set of materials that integrated logical skills and geological time and sequence; (2) implement these materials into the classroom instruction; and (3) test the effects on both geological achievement and critical thinking. Results show that a treatment group experienced significantly greater change than a control group in both critical thinking and geological achievement, demonstrating that college students can learn the complex rules of logical reasoning if those rules are presented in a manner understandable to them. In addition, the study demonstrates that college students are capable of applying these rules successfully in a setting such as geology. Although the full long-range impact of teaching logic as a reasoning tool has not yet been determined, the powerful implications such a tool has in increasing an individual's ability to think more critically and rationally are only beginning to manifest themselves in a wide range of possibilities. Future efforts need to focus on determining if this method can be successfully used in other sciences or with younger students. (JN)