Undercurrent typical of the continental rise which flows along the western boundaries of ocean basins. Such currents occur particularly in regions in which density stratification is strong because of the supply of cold waters originating near the poles. A well-known example is the Western Boundary Undercurrent which hugs the continental rise of eastern N. America. Contour currents are persistent, slow-moving (velocity 5–30 cm/s) flows capable of transporting mud, silt, and sand.