1. May be a natural bridge of bedrock normally formed outside a cave entrance by partial collapse leaving an isolated roof segment, as in the famous examples of Rakov Skocjan, Slovenia. Rock bridges may also occur inside caves due either surrounding phreatic dissolution or collapse between superimposed passages. Another common type inside a cave is a span of false floor where sediment is washed from below, as at The Bridge in GB Cavern in the Mendip Hills [9]. 2. In a cave, a residual rock span across a passage [10]. 3. In water wells, an obstruction in the drill hole or annulus. A bridge is usually formed by caving of the wall of the well bore, by the intrusion of a large boulder, or by filter pack materials during well completion. Bridging can also occur in the formation during well development [16]. See also natural bridge.