 To the south and east of the escarpment/plateau region, the folded mountains and alternating valleys are known as the Ridge-and-Valley Appalachians.These extend from the South of the Appalachians to northern New England save where cut by water gaps.In Northeastern Pennsylvania from the east of Harrisburg on the Susquehanna River, these ridge and valley features contain the richest and most widespread deposits of high energy clean burning anthracite coal in the world—the Coal Region—without which the industrial revolution in the United States would have been severely retarded and delayed.