The driving of a narrow roadway results in the development of a pressure arch over the excavation. The strata within the arch bend slightly and cease to support the overlying beds, and the load is transferred to the solid or rock along the sides. The wider the roadway, the greater the span of the arch and its height at the crown. A similar but larger pressure arch is formed across a longwall face, with one leg resting on the solid coal and the other on the solid pack behind the coal face.