Ductile (plastic) response of rock layers results in folds = permanent wavelike deformations in layered rocks (compressional forces, tensional forces, and shear forces see diagram in slides: ductile is bending . If you stretch it and it behaves in a ductile way, you will stretch it, but it will not break. Brittle response to stress results in faults = a fracture in bedrock along which rocks on one side have moved relative to the other side. The rock response to stress is influenced by a number of factors: type of stress, type of rock, temperature, pressure, fluids, length, magnitude of stress applied. Rockies and foothills: see diagram on slides this is a normal fault because hanging wall is moving down. Fault: brittle deformation, fracture with movement of rocks relative to each other and bedding is offset, lower pressure and temperatures.