Gap is a narrow valley or gorge cut by a stream across a ridge or mountain. If the river still occupies a gap, it is a water gap. If the river abandons it, the gap becomes a wind gap. Railroads and highways follow many gaps. The best-known examples of both types occur in the Appalachian Mountains. Harpers Ferry Gap, cut through the Blue Ridge by the Potomac River, is a water gap. The historic Wilderness Road, scouted by Daniel Boone, passed through Cumberland Gap, a typical wind gap in the Cumberland Mountains. See also Cumberland Gap; Delaware Water Gap.