Iron-rich sandstones in medieval churches in the Cambridge region, UK: distribution, sources and significance

England’s 13,000 medieval churches are a distinctive landscape feature, not least because they were mostly constructed of local building materials. Especially prominent are churches incorporating iron-rich (ferruginous) stone, in a range of yellow-brown colours. This study investigates churches in an 1,800 km2 area centred on south Cambridgeshire, and interprets the distribution of three iron-rich building stones in space and time.Over 120 churches have been studied in the field, and a further sixty churches provisionally assessed using only photographs. The study confirms existing views that two iron-rich walling stones — the Ely and Gamlingay sandstones — were quarried from the bedrock Woburn Sands Formation (Lower Cretaceous). However, a third walling stone — the Cottenham Sandstone — is re-interpreted as a ferricrete (ironpan) formed by cementation of Quaternary river sediments by iron-rich ground-water. The churches containing ferricrete are shown to lie on the relict floodplains of the ancestral River Cam, rather than following the Woburn Sands outcrop.Cottenham ferricrete was used most commonly during the twelfth to fourteenth centuries with some reuse in the fifteenth and sixteenth centuries. This result conflicts with a hypothesis based on churches in the London Basin that ferricrete walling indicates a twelfth-century or earlier date. There is no evidence in the Romanesque and later churches of the study area that iron-rich and iron-poor building stones were used to create patterned rubble walling as a visual feature. The lack of patterning supports the view that such walls were not meant to be seen and were usually rendered or lime-washed.