Wikipedia
Carrstone (or carstone, also known as Silsoe and gingerbread) is a sedimentary sandstone conglomerate formed during the Cretaceous period. It varies in colour from light to dark rusty ginger. Used as a building stone it can be found in Bedfordshire, Cambridgeshire and extensively in the historic buildings of North-west Norfolk.
Carrstone can vary in quality depending on factors such as the degree of iron oxide present, and sufficient pressure to form the matrix. Because of its variations it does not lend itself to carving or finer work. Carrstonework can be seen in buildings as: random carrstone, coursed carrstone, ashlared carrstone, all with, or without, galleting. Other patterns of use are: rough carrstone sipps (slips or brickettes) and cut carrstone sipps, both used in masonry fields between brickwork quoins. Cut carrstone sipps are used extensively at Sandringham House on the main building and the stables block. Other examples of carrstone work can be found on St Mary's Church, Barton Bendish as well as many other parish churches in the region. Hunstanton and Wolferton feature some interesting examples along with the 'Gingerbread Town' of Downham Market, notably the Grade II Listed Downham Market railway station.