According to Gowin, a curriculum properly derives its authority by representing the “criteria of excellence” for evaluating the claims produced within a field of inquiry. GowinÕs epistemology applied to examples from geological inquiry yields criteria of excellence responsive to the demands characteristic of geological problems. Student efforts to learn these criteria hold the promise of making progress toward independence in accessing, using, and evaluating knowledge. This understanding contributes to the reformation of the concept of inquiry as a “step beyond science as process” called for in the National Science Education Standards and reinforces the need to consider the diversity as well as unity of styles of scientific reasoning. Geological inquiries differ from those of other sciences because they refer to objects with histories. These histories create a demand for concepts that necessarily contain an irreducible element of ambiguity, thus permitting comparison and contrast of geological objects. A case study of how geologists apply analogies, impose boundaries on categories of thought, and constrain the ambiguity of key concepts in reasoning about the accumulation of sediments at a continental margin is used to support this argument. Such examples of geological reasoning support a skeptical attitude toward interdisciplinary curricula that omit or oversimplify criteria of excellence. © 1998 John Wiley & Sons, Inc. J Res Sci Teach 35: 189–212, 1998.