The dunes along the Dutch mainland coast consist of Old Dunes (ca 5000-0 BC) and Young Dunes (ca 0-1200 AD), which have been partly deposited over the Old Dunes. The Old Dunes consist of low parallel beach barrier ridges with old dune deposits and intermittent troughs. Since the 1850s large parts of the Old Dunes were excavated. Much of the sand was used to raise the soil for the layout of new extensions of growing cities like Haarlem and Amsterdam, which lie in the low polderland behind the dunes. The sand was sometimes mixed with peat and clay to form man-made culture soils that now lay between the dunes and the polderlands. The elevation of the flat lands is at a particular height above ground water. The soils proved to be very suited for the cultivation of various species of bulb plants, such as daffodils, tulips and hyacinths. In springtime these former dune areas turn into colourful blankets of red, yellow, purple and blue. The landscape is world famous and visited by many tourists. (Photograph by Frank van der Meulen, Delft, The Netherlands, Spring 2012.)