The geological constraints of the development of sandstone landforms in Central Europe, a case study of the Świętokrzyskie (Holy Cross) Mountains, Poland

• The crag formation is constrained by rock strength and gravity induced movements.
• Rock strength is conditioned by siliceous composition, porosity and compaction.
• Joint spacing and strata orientation are responsible for gravitational movements.
• Each crag-forming unit is characterised by specific lithological and structural features.

Eighty sites of crag groups and individual crags occurring in the Świętokrzyskie (Holy Cross) Mts., upland situated in central Poland, were described in detail in order to examine the lithological, structural, mechanic properties and the tectonic features of sandstones and quartzites representing six crag-forming lithostratigraphic units: Cambrian quartzites, Devonian quartzitic sandstones, Triassic and Jurassic sandstones. Specific features of these rocks are: their occurrence within the sequences consisting of different rock series, high energy depositional environments and siliceous composition. The cragforming rocks differ in the amount of cement (from strongly cemented quartzites to very porous sandstones with poor cement), which determines the diverse mechanical properties (from very strong to friable rocks). The crucial feature enabling formation of crags built of porous and friable sandstones is very dense grain packing due to chemical and mechanical compaction. Regarding the principal role of the gravitational disintegration of rock massifs under the periglacial conditions in the Late Pleistocene, other factors constraining the crag formation and shaping are: the tectonic situation of rocks (the orientation of strata and joints) as well as adequate joint spacing and bed thickness. Petrographic, structural and tectonic features are interrelated.