Many students enrolled in geoscience courses have poorly developed spatial skills that may impede their success in mastering geoscience methods and concepts. To illustrate the variety of spatial skills required in the geosciences, we analyze a hypothetical field day of a structural geologist from the perspective of spatial cognition. We discuss some of the cognitive processes required for selective geoscience tasks, including map reading, navigation, perception of orientation, measurement of strike and dip, and interpretation of spatial diagrams including cross sections and stereographic projections. We suggest teaching strategies for several spatially demanding geologic tasks. We also outline ideas for future interdisciplinary research that may contribute to the development and evaluation of curricula designed to improve students' mastery of geoscience and spatial thinking, and, simultaneously, contribute to the field of cognitive science.

Abstract Small intrusions (< km 2 ) on the margins of the Henry Mountains intrusive complex of southern Utah are exceptionally well exposed in three dimensions and have a variety of shapes. Our examination of the geometry, structures, and fabric of the Maiden Creek sill, Trachyte Mesa laccolith, and the Black Mesa bysmalith (cylindrical intrusion bounded by vertical faults) suggests that this range of intrusion geometry may reflect a continuum of igneous emplacement as volume increases through magma sheeting. Intrusions begin as thin sills and through incremental injection of additional sheets, inflate into laccoliths. Marginal wall rocks are strained and rotated upward. Further sheet emplacement leads to the formation of a fault at the margin of the inflating intrusion. This fault accommodates piston-like uplift of the intrusion’s roof and results in the formation of a bysmalith. All three of these intrusions exhibit evidence for sheeting, although the evidence is weakest on the margins of the Black Mesa bysmalith. Solid-state shear zones exist between sheets in the Maiden Creek sill and on the margins of the Trachyte Mesa laccolith. Cataclastic zones also separate sheets within the Trachyte Mesa laccolith. Evidence for sheeting in the interior of the Trachyte Mesa laccolith is solely based on differences in weathering and jointing patterns. Evidence for sheeting on the margins of the Black Mesa bysmalith is based on the differences in lineation patterns and also on the distribution of cataclastic zones.

G. K. Gilbert’s report on the Henry Mountains is classic for its contribution to knowledge of igneous structures, especially laccoliths, for its contributions to the understanding of geomorphic processes, and as an example of excellent technique in geologic reporting and writing. Present-day Ph.D. candidates and many of their faculty would do well to adopt Gilbert’s technique. His accomplishments are especially impressive when viewed in the perspective of the status of geologic knowledge at the time he did his work and the hazards accompanying his field work. His conclusions, seemingly elementary today, were received with skepticism by many of his contemporaries and were not fully accepted for about a quarter of a century. Modern surveys have confirmed his principal conclusions.

The scientific origins of Gilbert’s geomorphic model are explored, and the distinctive character of that model is compared with that of the rival model of W. M. Davis, with special importance being given to the role of negative feedback by Gilbert. The early development of Gilbert’s ideas (1871, 1875a, 1876) are treated, culminating in a detailed analysis of his classic work on the Henry Mountains (1877). His later work on coastal geomorphology, notably with reference to Lake Bonneville (1881, 1890) and on glacial geomorphology, showed a continuing preoccupation with the relations between form and process. An analysis of geomorphic work since World War II highlights the overriding importance of Gilbert’s recent influence, particularly over the application of systems philosophy to the environmental sciences.