A mine railway (or mine railroad, U.S.), sometimes pit railway, is a railway constructed to carry materials and workers in and out of a mine. Materials transported typically include ore, coal and overburden (also called variously spoils, waste, slack, culm, and tilings; all meaning waste rock). It is little remembered, but the mix of heavy and bulky materials which had to be hauled into and out of mines gave rise to the first several generations of railways, at first made of wooden rails, but eventually adding protective iron, steam locomotion by fixed engines and the earliest commercial steam locomotives, all in and around the works around mines.