As sand, soil or rock is eroded (worn away) from one place it has to end up somewhere else! When it settles we call this Sediment - which is taken by the action of wind, water, or ice, and/or by the force of gravity to a new place.
You can see this at the coast. Sand is sometimes washed off the beach so a sandy beach becomes stony, and that sand is washed somewhere else. On some beaches it settles just out to sea, to form a sandbank. Coastlines can change quite dramatically over a period of time as this coastal erosion occurs.
The BBC Bitesize website explains this well, but it's in the Key Stage 3 section (but then all Dorothy's readers are pretty smart, right?) but this little diagram explains the process well. I've changed the information so you can understand what happens.
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