A powerful spring, that in the middle ages was credited with religious significance, bursts out of the hillside near the town of Holywell and flows 3 km down the Greenfield Valley to the estuary of the River Dee. For many centuries the stream powered industrial concerns concerned with textiles, iron-making, paper-making and the processing of non-ferrous metals. In the late 18th century the valley was celebrated for its Arkwright-style cotton spinning mills, and for battery works making sheet and bolts from copper, smelted in Lancashire and Swansea from ores mined at Parys Mountain. A 28 ha country park has been created in the valley in which the remains of a succession of dams and the foundations of cotton mills and copper works have been preserved.