A eponynmous word from Paul Auster’s New York Trilogy. A macadam is a road, or the stones in a road, made up broken stones of even size, compacted together, and “bound with tar or bitumen” according the the O.A.D. It was invented by Scotsman John Laudon MacAdam and the standard form for paving roads pre-asphalt. A google image search shows various examples of the paving, but it is difficult to recognize without being able to inspect closely. Most paved and tar roads that do not use asphalt are macadam roads.