Deposition is the final step in the erosional-depositional system. Rock particles that are picked up and transported by one of the eroding agents will ultimately be deposited somewhere else, and agents of erosion become agents of deposition. Final deposition of particles (sediments) usually occurs at the mouth of a stream. This is due to the faster flowing stream emptying into a slower larger body of water. When deposition occurs at the mouth of a stream or river a process called horizontal sorting takes place. The sediments that were once carried down the stream are arranged from largest to smallest.

Factors Affecting Deposition
The major factors that affect the rate of deposition are particle size, shape, density, and the velocity of the transporting stream.

Size: The smaller particles settle more slowly than the larger particles, due to the pull of gravity. The smaller particles tend to stay in suspension for longer periods of time. This form of deposition is called graded bedding or vertical sorting. The diagram below shows graded bedding.

Shape: A round sediment compared to a flat (skipping stone) sediment of equal size will settle faster in a body of water. This is due to the resistance the flat particle will undergo as it settles through the water. The round particle will meet little resistance and settle at a must faster rate. The graphic below shows the relationship.

Density: The density of particles also influences the rates at which sediments settle out of running water and wind. If particles are the same size but have different densities the higher density particle will settle faster.

Velocity: The velocity of the transporting stream determines when sediments will be deposited. If the stream slows down during a drought period the carrying power will decrease and the particle sizes carried and deposited will also decrease. If a stream is flowing faster due to flood conditions then the carrying power of the stream will increase and the sizes of particles deposited will increase as well.

Glacial Deposition
Glacial ice deposits are very different from stream (water) deposits. Glacial deposits of gravel, boulders, and sand are unsorted with no layer as in graded bedding. Till which is the accumulation of sediments carried by a glacier is very sharp like broken glass. Again this is very different from stream sediments which are usually round and smooth due to abrasion.

The diagram below shows the unsorted nature of glacial deposits: