The mountain ranges of the Vienna Woods are the transition between the Eastern Alps and the Carpathians, separated by the Danube and some tectonic lines near Vienna. The northern area is part of the Alps' sandstone zone, while its south is part of the Northern Limestone Alps. In the east, the border is the thermal line, which forms a geological break line to the Viennese Basin. Beeches, oaks and hornbeams grow throughout the north of the Wienerwald forest; in the south are conifers, mostly pines and firs. The Föhrenberge (Pine Mountains) natural park is in the latter region.