Track ballast forms the trackbed upon which railway sleepers (UK) or railroad ties (US) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down vegetation that might interfere with the track structure. This also serves to hold the track in place as the trains roll by. It is typically made of crushed stone, although ballast has sometimes consisted of other, less suitable materials. The term "" comes from a nautical term for the stones used to stabilize a ship.