Track ballast forms the trackbed upon which railroad ties (sleepers) are laid. It is packed between, below, and around the ties.[1] 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.[1] Ballast also holds the track in place as the trains roll over it. It typically consists of crushed stone, although other, less suitable, materials have sometimes been used such as burnt clay.[2] The term "ballast" comes from a nautical term for the stones used to stabilize a ship