rag

Piece of hard, coarse-textured stone, capable of being broken into thick, flattish pieces, the commonest types being Kentish rag (tough, hard limestone, readily broken into usable pieces), Rowley rag (a basaltic stone from Staffordshire), and other stones, notably in the USA. Rag-stones are not laid in regular courses, and mostly used as facings to brick or other types of wall. Rag-stone’s appearance is net like, formed of a pattern of approximate polygons, with the mortar-joints coarse (rough-picked) or fine (close-picked)… Rag is also used in rubble walls. (Curl & Wilson, 2016)