In mid nineteenth-century Britain, the study of geology involved radical new understandings of the earth's history. This had ramifications for architecture, providing new ways of seeing stone and designing buildings. This article examines the works of stone-mason Charles Smith. Following the destruction of the Houses of Parliament in 1834, the government initiated a national survey to select a stone for Britain's new legislature. Alongside geologists Henry De la Beche and William Smith, Charles Smith toured the buildings and quarries of Britain, producing a report that was intended to guide not only the choice of stone at Westminster, but all future architectural projects. He spent the following two decades promoting geological knowledge for architectural work. His reading of texts that examined the earth's geological formation, such as Charles Lyell's, shaped new understandings of stone and cement. This article demonstrates how, in a rapidly industrialising society, geology and architecture became increasingly inseparable.