The sediments of the North Sea consist mainly of sands of Pleistocene origin derived from Fennoscandia and the Rhine River. The Straits of Dover were formed during the next to the last glacial period, as a result of the tremendous amount of water coming from the melting ice. At this time sandy sediments of Fennoscandian and Rhine origin were deposited as far west as the coast of France. The deposits on the floor of the North Sea now are essentially the same as they were during the Pleistocene, though locally they have been and are being shifted about slightly. Five types of provinces have been recognized petrologically in the North Sea. The most dominant type is of Fennoscandian origin. Along the coast of Belgium and Holland the submarine topography resembles barchane (du e) topography. These submarine barchanes are regarded as being formed by the strong ebb and flood tides in the area.