On its west, New Jersey is flanked by the Delaware River that forms its border with the Commonwealth of Pennsylvania and Delaware Bay which separates New Jersey from the State of Delaware. However, due to a fluke in a colonial land grant for the city of New Castle, Delaware (called The Twelve-Mile Circle), there is a small amount of Delaware territory in contiguous New Jersey. Finns Point, piers at Penns Grove, New Jersey and Pennsville, and Artificial Island, the tip of a small peninsula at Lower Alloways Creek are connected to Salem County. A coal pier in Logan Township also extends into the river. New Jersey's natural regions were formed by glaciers.