These small channels also act to distribute the stream's sediment load over the surface of the delta. Some deltas, like the Nile, have a triangular shape. Streams, like the Mississippi, that have a high sediment content and empty into relatively calm waters cause the formation of a birdfoot shaped delta . Foreset beds make up the main body of deltas. They are deposited at the outer edge of the delta at an angle of 5 to 25 degrees.
Steeper angles develop in finer sediments.
On top of the foreset beds are the nearly horizontal topset beds . These beds are of varying grain sizes and are formed from deposits of the small shifting channels found on the delta surface. In front and beneath the foreset beds are the bottomset beds . These beds are composed of fine silt and clay . Bottom set beds are formed when the finest material is carried out to sea by stream flow.