sentences:  Landscapes developed over Coal Measures rocks are extensively altered by man, as the coal and iron found within this thick sequence of rocks have long been economically important, particularly since the Industrial Revolution.The former coalfields of Flintshire, Denbighshire and South Wales are witness to this period.In South Wales, the Coal Measures are overlain by the thick sandstones of the Pennant Measures which often provides craggy edges to the plateau which has been deeply dissected to form the South Wales Valleys.