 This plan proved quite abortive, for the instant the wood gave way or yielded, the cast iron was broken, and it was found so useless and expensive that it was thrown aside altogether.Cast iron is rigid and brittle so that deflection of the rails resulted in breakages.In 1785 a wearing surface of Swedish malleable iron, 1¾ inches broad, and ¾ of an inch thick, was tried with great success because of its ability to flex with the timber.