Island is located in the Gulf of St. Lawrence, west of Cape Breton Island, north of the Nova Scotia peninsula, and northeast of New Brunswick. Its southern shore bounds the Northumberland Strait. The island has two urban areas, and in total, is the most densely populated province in Canada. The larger urban area surrounds Charlottetown Harbour, situated centrally on the island's southern shore. It consists of the capital city Charlottetown, the suburban towns of Cornwall and Stratford, and a developing urban fringe. A much smaller urban area developed around Summerside Harbour, situated on the southern shore 40 km (25 mi) west of Charlottetown. This consists primarily of the city of Summerside. As with all natural harbours on the island, Charlottetown and Summerside harbours are created by rias. The island's landscape is pastoral, with wooded areas and rolling hills. The coastline has a combination of long beaches, dunes, red sandstone cliffs, salt water marshes, and numerous bays and harbours. The beaches, dunes and sandstone cliffs consist of sedimentary rock and other material with a high iron concentration, which oxidizes upon exposure to the air. The geological properties of the white silica sand found at Basin Head are unique in the province; the sand grains cause a scrubbing noise as they rub against each other when walked on, and have been called the "singing sands". Large dune fields on the north shore can be found on barrier islands at the entrances to various bays and harbours. The sand dunes at Greenwich are of particular significance as the shifting, parabolic dune system is home to a variety of birds and rare plants, and it is also a site of significant archeological intere