Track ballast forms the trackbed upon which railroad ties (sleepers) 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 to keep down vegetation that might interfere with the track structure. The ballast also holds the track in place as the trains roll over it. It consists of crushed stone. The term “ballast” comes from a nautical term for the stones used to stabilize a ship.
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated, although there are exceptions. In geology, the term marble refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone.