Clay Formation) of the Aalenian subdivision of the Jurassic Period, which is named after Aalen. On the Sandberg, the Schnaitberg and the Schradenberg hills, all in the west of Aalen, the Eisensandstein (Iron Sandstone) formation emerges to the surface. On the other hills of the city, sands (Goldshöfer Sande), gravel and residual rubble prevail. The historic centre of Aalen and the other areas in the Kocher valley are founded completely on holocenic floodplain loam (Auelehm) and riverbed gravel that have filled in the valley. Most parts of Dewangen and Fachsenfeld are founded on formations of Jurensismergel (Jurensis Marl), Posidonienschiefer (cf. Posidonia Shale), Amaltheenton (Amalthean Clay), Numismalismergel (Numismalis Marl) and Obtususton (Obtusus Clay, named after Asteroceras obtusum ammonites) moving from south to north, all belonging to the Jurassic and being rich in fossils. They are at last followed by the Trossingen Formation already belonging to the Late Triassic. Until 1939 iron ore was mined on the Braunenberg hill. (see Tiefer Stollen section). Extent of the borough The maximum extent of the town's territory amounts to in a north–south dimension and in an east–west dimension. The area is , which includes 42.2% agriculturally used area and 37.7% of forest. 11.5% are built up or vacant, 6.4% is used by traffic infrastructure. Sporting and recreation grounds and parks comprise 1% , other areas 1.1% . Adjacent towns The following municipalities border on Aalen. They are listed clockwise, beginning south, with their respective linear distances to Aalen town centre given in brackets: Oberkochen (), Essingen (), Heuchlingen (), Abtsgmünd (), Neuler (), Hüttlingen (), Rainau (), Westhausen (), Lauchheim (), Bopfingen () and Neresheim (), all in the Ostalbkreis district, furthermore Heidenheim an der Brenz () and Königsbronn (), both in Heidenheim district. Boroughs Aalen's territory consists of the town centre (Kernstadt) and the municipalities merged from between 1938 (Unterrombach) and 1975 (Wasseralfingen, see mergings section). The municipalities merged in the course of the latest municipal reform of the 1970s are also called Stadtbezirke (quarters or districts), and are Ortschaften ("settlements") in terms of Baden-Württemberg's Gemeindeordnung (municipal code), which means, each of them has its own council elected by its respective residents (Ortschaftsrat) and is presided by a spokesperson (Ortsvorsteher). The town centre itself and the merged former municipalities consist of numerous villages (Teilorte), mostly separated by open ground from each other and having their own independent and long-standing history. Some however have been