In geology, transportation refers to the movement of eroded debris, whether by rivers, glaciers, wind or ocean currents and tides. Particle sizes can vary from tiny clay particles suspended in moving water, to pebbles and boulders. As the particles are transported, their edges can be smoothed, and is described as rounding. Deposition occurs when the speed of movement of the transporting medium becomes insufficient to hold the particles. Examples of such deposits are: Bunter, Moraine, Overbank, Dunes, Tombolo.