Tuff, also called travertine, is a rock of sedimentary origin composed of calcareous concretions. Its complex formation results from a chemical reaction in which the carbon dioxide released by the water is used by plants during the precipitation of calcium carbonate. This dissolution of the carbon ions and their association with certain plant formations give a so-called chlorophyll precipitation also conditioned to the quantity of water. Beyond the physicochemical process, it is therefore the living structures (bryophyte, algae) which allow the crystals to bind together like here in the Tufs waterfall of Planches-près-Arbois.