the Middlesboro Syncline. The once flat-lying sedimentary rocks were deformed roughly 40 degrees northwest. Further constriction to the northwest of Cumberland Mountain developed into a fault trending north-to-south called the Rocky Face Fault, which eventually cut through Cumberland Mountain. This combination of natural geological processes created ideal conditions for weathering and erosion of the rocks. The discovery of the Middlesboro impact structure has proposed new details in the formation of Cumberland Gap. Less than 300 million years ago a meteorite, "approximately the size of a football field", struck the earth, creating the Middlesboro Crater. One of three astroblemes in the state, it is a diameter meteorite impact crater with the city of Middlesboro, Kentucky built entirely inside it. Detailed mapping by geologists in the 1960s led many to interpret the geological features of the area to be the site of an ancient impact. In 1966 Robert Dietz discovered shatter cones in nearby sandstone, proving recent speculation. Shatter cones, a rock-shattering pattern naturally formed only during impact events, are found in abundance in the area. The presence of shatter cones found also helped confirm the origin of the impact. In September 2003, the site was designated a Distinguished Geologic Site by the Kentucky Society of Professional Geologists. Without the Rocky Face Fault, it would have been difficult for pack-horses to navigate this gap and the gap in Pine Mountain near Pineville, and it would be improbable that wagon roads would have been constructed at an early date. Middlesboro is the only place in the world where coal is mined inside an astrobleme. Special mining techniques must be used in the complicated strata of this crater. History The earliest written account of Cumberland Gap dates to the 1670s, by Abraham Wood of Virginia. Some time before 1748 Samuel Stalnaker is believed to have passed through the gap while exploring the region. The gap was named for Prince William, Duke of Cumberland, son of King George II of Great Britain, who had many places named for him in the American colonies after the Battle of Culloden. The explorer Thomas Walker gave the name to the Cumberland River in 1750, and the name soon spread to many other features in the region, such as the Cumberland Gap. In 1769 Joseph Martin built a fort nearby at present-day Rose Hill, Virginia, on behalf of Walker's land claimants. But Martin and his men were chased out