The term 'paving substance' can refer to two different materials: TAR and MACADAM. TAR is a dark, viscous material made from the destructive distillation of organic matter such as wood, coal, or peat. It is often used in road construction and roofing. MACADAM is a type of road construction that uses small stones, usually crushed stone, bound together with TAR or asphalt. It is a cheaper alternative to concrete and asphalt and is often used for low-traffic roads.