The karst geo-morphology is usually characterized by dolines (sinkholes), hums (towers), caves, and a complex subsurface drainage system. Karstification is the geologic process of differential chemical and mechanical erosion by water on soluble bodies of rock, such as limestone, dolomite, gypsum, or salt, at or near the Earth's surface. Karstification is exhibited best on thick, fractured, and pure limestones in a humid environment in which the subsurface and surface are being modified simultaneously. The term ""karst"" stems from the region Krs in Slovenia which is typified by stony barren rock. The Indo-European word ""kar"" for rock and the Italian word ""carso"" evolved to the Germanized term ""karst,"" which is now the accepted term for solution-derived landscapes like those just north and east of the Adriatic Sea.