Petrovic, A.S. and Carevic, I.Z. 2015. Geological influence on the formation of Samar natural bridge and collapse valley of Ravna River from the NE Kučaj Mountains (Carpatho-Balkanides, eastern Serbia). Acta Carsologica. 44, 1 (Jul. 2015). DOI:https://doi.org/10.3986/ac.v44i1.898.