In 1878, Albert Heim published a monograph on the structure of the Tödi-Windgällen Range (eastern Helvetic Alps, Switzerland) containing a section entitled “The mechanical transformation of rocks during mountain building,” which is a survey and synthesis of structural geologic principles of remarkably modern tone, the prototype of many modern textbooks. Starting from basic concepts and questions–stress, strain, strength, state, pressure, brittle versus ductile behavior–Heim surveyed the results of rock deformation in nature in order to arrive at a general theory of mountain building. A complete spectrum of the minor structures resulting from fracture and flow in the Earth's crust was reviewed, and their relation to major structures was discussed. The morphology of folded layers and the distribution of minor structures in large-scale folds were combined with a clear concept of competence to interpret the mechanism of folding in the area studied. Heim showed that the distribution of brittle and ductile features in space, combined with physical theory and experimental data, support the concept of the latent ductility of all rocks below a certain depth in the Earth's crust and the idea of “lithostatic” pressure. These and other aspects of his theory raise the question, How did it take 100 years to accomplish our relatively modest advance in understanding?